From naked mole rats to elephants, research in wildlife biology increasingly entails interference with individual animals, and there are innumerable reasons to justify this interference for the proper management of populations. As Boyd (2002) has emphasized, however, there is a central question about the extent to which it is reasonable to intervene in a population when the species is endangered. This comment arose as part of a debate published last year in this journal on the possible harmful effects of immobilizing black rhinos and fitting them with radio-collars. Alibhai, Jewell & Towindo (2001) had prompted the debate with a discussion on the possible reduction of fertility in black rhinos caused by immobilization followed by an account of the wounding of a rhino by an ill-fitting radio-collar (Alibhai & Jewell, 2001).