In this issue of Animal Welfare for the first time we have included an Invited Essay. These essays are to be occasional features on contemporary welfare problems; written at the invitation of the editor and refereed. The first is by Trevor Poole, a mammal behaviour zoologist with an active interest in laboratory animal science and welfare, considering the new and controversial subject of transgenic animals. In this fast moving field relatively little thought has been given to the possible suffering which transgenic animals may be enduring for human benefit.