Using animals in medicine tests is a big issue.
Some people think it's cruel, others reckon it's needed to develop medicines that will save lives.
Scientists who carry out tests on animals say they're closer to finding a cure for glue ear - something which affects lots of children.
Newsround's Laura visited a lab to find out more.
But we want to know what YOU think.
E-mail and let us know!
Unfortunately this topic is now closed but there are Comments pages on other subjects on the main Chat index.
I think animal testing is wrong because the animals might be in pain and they can't tell us!
Kayley, 11, Yorkshire
I think it is wrong to test anything on animals, it does not matter what animal it is - a rat, monkey, dog or rabbit. It is not right to abuse them like that and they don't deserve to die in a horrible way.
Kellie, 14, Edinburgh
I don't know because on the one hand it helps saves people lives but it also kills animals.
Fionn, 10, Cambridge
I think that testing on animals should be done because if a human died everyone would be upset.
Ellie, 10, Portsmouth
I think animal testing is bad, but I wouldn't care if scientists were doing experiments on rats. I don't like rats so, it doesn't matter to me, unless it was a dog, or any other animal.
Sarah, 12, USA
I think animal testing is unfair on the poor animals that are involved. They don't get a choice and some of them die from some of the things they do to them.
Lauren, 10, Swindon
We don't have to do it. I think we shouldn't make these medicines if we have to hurt animals.
Alice, 9, Wigan
I have mixed feelings. I think it's cruel, but on the other hand what choice do we have?
Ellie, 14, Oxfordshire
I think animal testing is cruel because animals have rights too, even rodents. I'd rather be ill than treat animals with disrespect.
Kate, 9, Oman
I think animals deserve respect and it is not right to abuse them just to save humans. Just because humans wouldn't volunteer to be tested on doesn't mean that animals would if they had a choice.
Georgina, 11, Scarborough
I think that animal testing is ok if it is very necessary. But I think they should always look after the animals properly and also try to find other ways to test medicine.
Hayley, 13, Manchester
I think it is important to do testing but then I would say this because my sister has an illness animal testing could help.
Eleanor, 12, Witney
I think that animal testing for cosmetics is wrong. I've seen pictures of how these animals suffer, but I'm not sure about testing medicines on them.
Katrina, 11, Newton Abbot
I know in the back of my mind animal testing is wrong but if it was a choice between a million mice and my family it would be my family every time.
Natasha, 13, Melksham
I think it's really cruel because I don't think you're treating animals with respect.
Laura, 11, Teignmouth
I think that it is a cruel thing to do to little animals but on the other hand we do need to check if are medicines are ok. So really it is a hard choice.
Sophie, 11, Bristol
I think it is fair in one way and not in another.
It's hard as I have a pet mouse and so I feel sorry for mice that are being testing on, but it does help save people lives.
Joanna, 8, London
Animal testing is cruel, the only things we should test on animals are products like animal food.
Callum, 11, Doncaster
Animal testing is needed. I'm sure most the people against it would have a different view if they became seriously ill and the medicine used to treat them had been tested on animals.
Animal testing is not morally right, but without it many more humans would die.
Owen, 12, Birmingham
I think animal testing is wrong. Although it helps save us from various illnesses, it's not fair that the animals don't get a choice as they can't say no!
Laura, 12, South Wales
I think that it is fine to test on animals as long as that is all they are doing to them. I would rather a animal was tested than somebody in my family dying.
Ellie, 12, Berkhamsted
I think animal testing should be stopped. Even though we need to test medicines, animals have feelings too.
Jessica, 12, Stoke-on-Trent
I think it is okay that we test on animals, because if we didn't I doubt many humans would want to do it!
Remi, 10, Southend on Sea
I don't care what anyone says, animal testing helped save my dad's life.
Ben, 13, Sawtry
I think animal testing is cruel and I feel sorry for the animals.
Helen, 9, Kilwinning
I think testing on animals is necessary for things like medicine, because if people want to have medicine that won't harm them they need to have them tested on animals first.
Sarah, 13, Hawkshead
If we can't test on animals, what can we test things such as medicine on?
I don't think animals should be tested on because they can't have their say on it.
Elanor, 12, Hawarden
I think it is despicable and that all animal testing should be banned.
Oceane, 12, Lichfield
I think animal testing is a harsh way to find out cures for illnesses but it is needed otherwise how else would we find out cures?
Rosie, 11, Wolverhampton
I think animal testing is okay if they are being tested for cures for illnesses but why should they be tested on for beauty products?
Christy, 12, Maidstone
I think it is cruel to test on animals. However it needs to be done to cure diseases, but testing on rats isn't as bad as testing on dogs or apes.
Michael, 12, Birmingham
Animals are just as important as us, so why do we test on them? Why not just test on ourselves?
Bradley, 12, Farnham
I love animals and I think it's really unfair for them to test human products on them. I say: "if they're made for humans
let them be tested on humans!"
Sarah, 13, Cardiff
Animal testing is so wrong and putrid!
Emery, 10, USA
I think it is cruel to test make-up on animals but animal testing does save hundreds of lives when they use them for medical tests. Although I do think we should only test on rats or mice as they are plentiful and they are rodents.
Catriona, 13, Ballynahinch
I think that it is good because it can save human lives and help find cures for diseases.
Michelle, 12, Ireland
I think it's important to have these tests because they could cure diseases like Aids and cancer.
Jo, 12, London
I don't like cosmetics testing on animals but I think medical testing is alright. Some people who say it is cruel can be hypocritical because they will get a flu or cold and they will probably use medicines that at some point have been tested on animals! Animal testing does saves lives.
Erin, 14, Oban
Animal testing for cosmetic reasons is cruel and for medical conditions it is not ideal but no other options are currently available. More needs to be done to make sure animals used for medical testing receive the best possible care and humane treatment.
Violet-Mae, 8, Selsey
I think animal testing is cruel. I'd rather be ill then treat animals with no respect - they have feelings too!
Sophie, 13, Wokingham
I think there's no right and wrong answer because yes it is cruel but we need to do it to cure diseases.
Laura, 14, Chesterfield
I think it's a load of rubbish. Why should lovely cats and dogs and other animals be used to "help" humans? We've done enough damage to nature during our history, why can't we leave them be? These animals are being destroyed - just look at the image of the cats above, it makes me cry.
Caoimhe, 13, Italy
I think it's really really cruel to animals. They need respect and so what if it develops new medicines, they have feelings too.
Rae, 10, Singapore
I believe in animal testing as without the use of animals medicine would be in the 'dark age' and people. It is them who give us the chance of life but they do require respect and should be treated as humanely as possible.
Harry, 12, Aviemore
I don't like it but many people would be sick if animal testing didn't happen. But animals are not always treated well and that is not good.
Maria, 13, Denmark
Animal testing is unfair, especially when it comes cosmetics but I CAN understand when it comes to testing medicines.
Amy, 14, Northern Ireland
Animal testing has to be done because we share loads of our genes with them and also, do you really want to have to experiment on humans?
Osnat, 10, London
I think animal testing is cruel, especially the way they keep the animals in tiny cages with nothing to do all day.
Lily, 11, France
It's horrible. What did the animals do to us? If it's to test medicine for humans then it should be tested by humans.
Robyn, 12, Sittingbourne
I really do not agree with this because what they do to animals is dreadful and it must be stopped - NOW! It makes me so upset to see they type of things they do to them.
Louise, 13, Liverpool
I really believe in animal rights and I think it is very cruel to do tests on animals because it means they could be at risk of dying.
Anna, 9, Spebbing
I think it is cruel but if they didn't use animals there wouldn't be cures for diseases. But there is no need to test things like make-up on animals because make-up is not an essential thing to live with like medicines.
Nicole, 10, Scotland
I think it's horrible. Animals are the nearest things to people and so we have got show them some respect.
Orla, 13, Cork
I feel sorry about animals being tested on because some are still very young.
Halima, 9, Blackburn
I think we shouldn't test make-up on animals as it's really bad for them.
Kiwi, 11, Ireland
I think animal testing is cruel.
James, 7, Newport
I think it's terrible and cruel and we should
try another way because when the people test on animals some of the animals get killed.
Kathryn, 14, Nuneaton
I think animal testing is very cruel. I am an animal lover so I think they need to find a less cruel way to testing new medicines.
Hayley, 11, Huntingdon
I'm sorry for the animals, but it's important to have these tests because they could cure diseases like cancer.
Katie, 10, Brighton