Experts say experiments on animals are needed to find cures for devastating diseases.
But campaigners say too many animals are being used unnecessarily and scientists aren't looking for alternatives to testing on animals.
Testing types
As well as medicines, animals are used to test out cleaning products, pesticides, food additives and other chemicals. But testing cosmetics on animals was banned in the UK in 1997.
Many of the experiments involve brain injections and skin irritation tests.
Scientists are now being asked to continue to look for alternative ways of testing products.