Hollywood couple Katharine Hepburn and Spencer Tracy were the best on-screen lovers, according to a study by the Royal Society of Chemistry.
Spencer Tracy was the love of Hepburn's life
The society found Hepburn's fiery persona and Tracy's laid-back approach complemented each other.
"Like anything to do with chemistry, it is all about mixing up a cocktail of ingredients to get the right result," said a society spokesman.
Another real-life couple, Elizabeth Taylor and Richard Burton, came second.
TOP FIVE ON-SCREEN DUOS
1. Spencer Tracy and Katharine Hepburn - Adam's Rib and Guess Who's Coming To Dinner
2. Elizabeth Taylor and Richard Burton - Cleopatra and Who's Afraid of Virginia Woolf?
3. Humphrey Bogart and Lauren Bacall - The Big Sleep and Key Largo
4. Mel Gibson and Danny Glover - Lethal Weapon series
5. Robert Redford and Paul Newman - Butch Cassidy and the Sundance Kid and The Sting
Source: Royal Society of Chemistry
Humphrey Bogart and Lauren Bacall were third in a top ten of top film double-acts which did not include any films from recent years, apart from the Lethal Weapon series.
"With men and women it can be the chemical reaction of love, with pheromones and other hormones being released and the two obviously attracted to each other,
which translates well to the audience," said the Society spokesman.
While four all-male duos made the grade, there were no all-female pairings included.
The study said some couples produced a negative reaction, such as the pairing of Marilyn Monroe with Laurence Olivier in The Prince and the Showgirl.
The society also pointed out several modern film couples whose chemistry just did not gel - Hugh Grant and Andie McDowell in Four Weddings and a Funeral fell flat, as did Sean Connery and Catherine Zeta Jones in Entrapment.
The spokesman added: "People assume on screen chemistry is just two good actors doing their job, but it isn't as several examples have shown. Just look at Madonna and anyone she has acted with, for instance.
"It is about ingredients, characteristics and personality traits.
"It can be a physical thing like that of two lovers or a humour-based friendship, such as Jack Lemmon and Walter Matthau where you just know,
as a viewer, that the two of them are great mates in real life too," he added.
Which film duo do you think had the best on-screen chemistry? Here is a selection of BBC News Online users' views.
Agree about Laurel & Hardy, but also pretty good were Bogart and Hepburn in The African Queen. Bang up to date, Robert Duvall and Kevin Costner in Open Range.
Mike Rollings, Haywards Heath, Sussex
Johm Wayne & Maureen O'Hara in McLintock, western version of Taming of the Shrew.
Fiona Waland, Telford
Owen Wilson and Ben Stiller of course, the best on-screen double act since Lemmon and Matthau, and what about Ethan Hawke and Julie Delpy in Before Sunrise?
I agree with Tracy and Hepburn but what about Julie Christie and Donald Sutherland in Don't Look Now? Apparently they had to be pulled off each other during filming.
Richard Hughes, Didcot, Oxon
Best example of friendship between two men (boys) would be Stan and Kyle in Southpark, because they laugh at the same things, and with few words understand each other. The most genuine romance on screen, which actually also took place behind screen and ended up in marriage is Val Kilmer and Joanne Whalley-Kilmer in Willow.
Pieter, Oxford, UK
Gene Wilder and Richard Pryor.
Brett Hunter, Cambridge, UK
Butch and the Kid! Paul Newman and Robert Redford. A film that rarely makes it in top listings - I can't imagine why. The chemistry was a key ingredient.
D Connolly, Luton, Bedfordshire
Richard Burton and Elizabeth Taylor in Cleopatra. The film was dire but the chemistry was real! In the end they left their respective partners for each other!
Kate, Wouldham, Kent
Sandra Bullock and Hugh Grant were fantastic in Two Weeks Notice but the all time high for on screen chemistry has to be Deborah Kerr and Cary Grant in An Affair to Remember. Wow!
Trish, Portsmouth, UK
Jodie Foster and Anthony Hopkins in Silence of the Lambs - scary!
Al Pacino and Robert De Niro in Heat, throughout the entire film you get the sense of two guys at opposite ends of the spectrum undeniably bonded together through the similarities of their different lives - explosive!
Brian Mullin, Belfast
Harrison Ford and Anne Heche in 6 Days 7 Nights. Very funny. Similar to Meg Ryan and Kevin Kline in French Kiss. Hilarious!
Chris F, London
Jay and Silent Bob - that's pure sympatico!
I think that Alan Rickman and Juliet Stevenson had great chemistry in Truly Madly Deeply. They brought you right into the film, brilliant!
Charlotte Hobson, Leeds, UK
Audrey Tautou and Mathieu Kassovitz in Amelie. I almost melted when she did. To have so much tension through a door too....tingling.
Sarah, Glasgow, Scotland
It has to be James Stewart and his best pal Harvey - ok we couldn't see him but wasn't it the most potent screen double ever?
Julie Jarvis, Birkenhead
Sarah Michelle Gellar and David Boreanaz in Buffy The Vampire Slayer.
Clint Eastwood and Lee Van Cleef in A Few Dollars More.
Simon D, London
Ben Stiller and Owen Wilson - Zoolander, The Royal Tenenbaums, Starsky & Hutch, etc.
Tom Cruise and Penelope Cruz in Vanilla Sky. Did those two have the hots for each other or what?! It's obvious in every single scene they share.
Neil R, London
A really modern pairing is Simon Pegg and Nick Frost in both Spaced and Shaun of the Dead. Two great friends in real life and it comes across in their acting. Marvellous.
Elly G, Manchester
My favourite chemistry of all time has to be Nicholas Cage & Elizabeth Shue in Leaving Las Vegas.
Is this possible?
Could it be that not a single one remembers the electrifying chases, the loveable expressions of pain (literally) of Tom and Jerry! I mean... they were made for each other. The chemistry - well, the flying sauce pans and mouse traps say it all.
Varj, London, UK
Buzz and Woody in the Toy Story films - even though they're only pixels.
Jen B, Newcastle, Staffs
Harrison Ford and Peter Mayhew (Han Solo/Chewbacca in Star Wars episodes IV-VI) have left an indelible imprint on the psyche of millions. Has there ever been a more affecting portrayal of cross species, same sex and apparently platonic bonding on the silver screen? I think not.
Wayne Drudge, Slough
Rita Hayworth and Glenn Ford in Gilda. Scorches the paint off the walls every time you see them.
Richard, London, UK
Dom de Luise and Burt Reynolds in the Cannonball Run. Surely the magnum opus of two stars at the height of their powers.
Wayne Drudge, Slough
It was a strange relationship and one I hadn't seen the like of in cinemas beforehand (although I have seen it since in other films) - Clarice Starling and Hannibal Lecter. In Silence of the Lambs of course. Not in Hannibal.
Honourable mention to Joe Pesci and Marisa Tomei in My Cousin Vinny.
richard, Birmingham, England
Kermit the Frog and Miss Piggy have to take the honours for having a very distinct on-screen chemistry!!
Gary Skinner, Watford, UK
Cybill Shepherd and Bruce Willis in Moonlighting, pre- consummation episodes.
Wayne Drudge, Slough
Bill Murray and Scarlett Johansson in Lost in Translation. Despite the age difference, you could almost physically feel the chemistry between them.
Suzanne Fry, Welwyn Garden City, UK
It has to be Laurel and Hardy, surely!
Lorraine Berkshire, Oxford, England
Gregory Peck and Audrey Hepburn.
Alia, London, UK
Jennifer Lopez and George Clooney in Out of Sight - perfect!
I think you're forgetting the incredible pairing of brains and brawn, of wit and charm, of big and small. Yes, I am talking about the undeniable chemistry that existed between Arnold Schwarzenegger and Danny Devito in the 80s classic Twins and also later on in Junior. Classic.
Ryan Prosser, Barry, Wales
It has to be Tom Hanks and Meg Ryan. Can't get any better than Sleepless in Seattle, You've Got Mail or Joe Versus The Volcano. Don't forget Ronald Reagan and that chimp from Bedtime For Bonzo.
D Fresh, Los Angeles, USA
It's got to be Ben Affleck and Jason Lee in Chasing Amy. The movie shows just how much two best friends can care for each other and nobody else could have pulled off those performances.
Pete, Doncaster, UK
Humphrey Bogart and Lauren Bacall had the best male/female chemistry ever. Sad no female/female pairings made the grade - what about Susan Sarandon and Geena Davis in Thelma and Louise?
Catriona, Glasgow, Scotland
Emma Thompson and Anthony Hopkins as Miss Kenton and Mr Stevens in The Remains of the Day. Two great Brits coming together to produce a heart wrenching story of lost love.
Alasdair Ross, Cambridge, UK
Fred Astaire and Ginger Rogers, Bob Hope and Bing Crosby, Laurel and Hardy, some of my favourite couples of all time. I am also forgetting the legends of Morecombe and Wise.
Dilip M, Leics, UK
Eddie murphy and Nick Nolte - 48 Hours.
Dean Martin and Jerry Lewis. Comical and sweet!
I think the most explosive chemistry I've seen on screen was Paul Newman and Elizabeth Taylor in Cat on a Hot Tin Roof. The tension is so palpable it's scary!
C. Faniadis, BXL, Belgium
How can they have forgotten Steve McQueen and Faye Dunaway in the original Thomas Crown Affair?
Andy Trombala, United Kingdom
Ewan McGregor and NIcole Kidman in Moulin Rouge. Could feel their chemistry throughout the film.
Ben Walker, Bournemouth, England
Although they were not "lovers" per se, the pairing of Marlon Brando's gruff, animalistic Stanley Kowalski against Vivien Leigh's vulnerable and delusional Blanche DuBois in A Streetcar Named Desire was absolutely and brutally electrifying.
Andrea Tsai, London, England
One of my favourite pairings was Tony Curtis and Jack Lemmon.
Jeannie Warnock, Montreal, Canada
Wallace and Gromit have the best on-screen chemistry, who else could visit the moon, save a flock of sheep and capture a dangerous criminal like feathers McGraw!!!
The best chemistry in film history has to be Mr Wint and Mr Kidd from Diamonds are Forever played by Bruce Glover and Putter Smith. It was heartwarming, moving and a glowing tribute.
Joseph McBurney, London, UK
Katharine Hepburn and Spencer Tracey were two of the greatest film idols of all time. Their off-screen love affair was so apparent in their on-screen chemistry, making them a delight to watch.
Cary Grant and Grace Kelly in To Catch a Thief - smouldering!
My favourite onscreen pairing has got to be Doris Day and Rock Hudson. There was a completely charming chemistry between them, and hilarity always ensued in their movies.
Chera, Toronto, Canada
I think Audrey Hepburn & Gregory Peck were very lovely and classy as ill-fated lovers in Roman Holiday.
Margaret, Hong Kong
Alan Arkin and James Caan in Freebie and the Bean. The first cop buddy movie, and the template for all that followed.
Guy Matthews, UK
I love Ken and Emma in Much Ado About Nothing. But that's Shakespeare for you!
Pete, Southend on Sea, Essex
Mulder and Scully in The X Files.
Ann Alexander, Nantwich, Cheshire
How about Richard E Grant and Paul McGann in Withnail & I - superb!
Keith Denham, Darlington, UK
Julia Roberts and Richard Gere in Pretty Woman - a modern classic.
The best couple is Ethan Hawke and Winona Ryder in Reality Bites, ouahhh.
Ariane Basaguren, London, UK
Surely Thelma & Louise make the cut for an all-female pairing!
Nick, London, UK
Even though I myself was born barely a mile from the house where Stan Laurel was born (surely one half of the ultimate all-male partnership), I feel the award for best on-screen chemistry between couple lies elsewhere. Namely the ultimate married couple, Homer & Marge Simpson. She loves him despite all his many faults and he loves her in return for feeding him and washing his underwear.
Dominic Allonby, Ulverston, England
Ben Stiller and Owen Wilson in every film they've been in together.
Samuel L Jackson & John Travolta in Pulp Fiction.... Royale with Cheese!
Rich P, York