This is a difficult question that understandably raises strong emotions. Some animal research has yielded significant benefit to humans, in drug development and in many other areas. But these human benefits have been purchased at the cost of animal harms, and it is natural to worry whether this is fair.

Some people are reassured about the morality of animal experimentation by the fact that we kill so many more animals for meat than we do for research, or by the fact that more rodents are killed by cats than by scientists. But it is not clear that we should be morally reassured by these facts.

Some would argue that even though animal suffering is bad and morally significant, animal death is does not have the same moral significance as human death, because of various abilities that humans have to conceptualise and to anticipate that animals lack. So one might be able to justify killing animals in experiments, if their suffering is sufficiently low. (Similarly, one might think that it is morally permissible to eat free range chicken but not factory farmed chicken.)

The Nuffiield Council on Bioethics has recently published a helpful report entitled The Ethics of Research Involving Animals. (I should declare an interest: I am a member of the Nuffield Council, though I was not on the working party that produced this particular report.)