Sir Anthony Hopkins has said Gwyneth Paltrow ranks alongside Jodie Foster as "spectacular" and "the most brilliant actress I have ever worked with".
By Victoria Lindrea
BBC News entertainment reporter in Venice
He was speaking at Venice Film Festival about his Proof co-star Paltrow, but she could not attend after her plane was unable to take off in New York.
"I've worked with two great actresses - Jodie Foster and Gwyneth Paltrow," he told journalists.
Speaking via mobile phone, Paltrow said she was "heartbroken" not to be there.
Sir Anthony plays Gwyneth Paltrow's father in Proof
"I had an extraordinarily unpleasant evening last night trying to get there," she said.
Sir Anthony, who appeared with Foster in 1991's Silence of the Lambs, added his compliments about Paltrow were "not just giving you the usual actor's charming answer".
Based on the Pulitzer Prize-winning play by David Auburn, Proof sees Paltrow return to a character she first played on the West End stage in 2002.
Since then she has married Coldplay singer Chris Martin, had a daughter and lost her father, film director Bruce, to throat cancer.
"I feel I came to the film as a different person," said Paltrow, who fell pregnant shortly before shooting began.
The veteran actor was accompanied by co-star Jake Gyllenhaal
"When we did the play, my father was alive and I was single.
"When it came to the film, I had lost my father but been blessed with wonderful things in my personal life.
"My father's death gave me an insight into the reality of death and grief - and the finality of it."
Paltrow said she was initially reluctant to return to work after giving birth to baby Apple.
"Once I had my daughter, I was very reticent to leave her.
"I finally went back to work when she was 10 months old, to do a small role.
"It was fantastic and exhilarating, but I was torn - not being the person to put my daughter to sleep at night."
Paltrow said she chooses her parts more carefully so she can spend as much time as possible with her family.
"I can no longer just pick up and head out to a remote location. I am looking for roles that will enrich me as an artist, a person and a mother."
Sir Anthony Hopkins told journalists he had taken more than a year off work before accepting his role in Proof as a mathematical genius whose daughter may have inherited his mental instability.
Gyllenhaal plays an ex-student who falls for Paltrow's character
"I accepted because I play an interesting man - a maths professor who has a complete mental breakdown," he said.
The Welsh-born actor, now a US citizen, also had praise for director John Madden.
"With John there's no fuss. He knows exactly what he wants to do."
The 67-year-old arrived at the press conference with actor Jake Gyllenhaal, who plays a former student of Hopkins' character.
Gyllenhaal also appears in Ang Lee's western Brokeback Mountain, which screened at Venice last Friday.