Sir, The workings of the Animals (Scientific Procedures) Act 1986 (Reports and comments, Animal Welfare 1993, 2: 90-92) rightly drew attention to the difficulty of using the Home Office Statistics of Scientific Procedures on Living Animals. Such concerns are not new and are shared by protagonists on both sides of the present debate over the use of animal experimentation in the UK. Indeed, commenting on the 1991 publication, Hart has argued that: ‘Doctors wanting to defend Britain's 3.2 million scientific procedures on living animals will want to know much more about what they are defending than this book tells them.’ (British Medical Journal 303: 670).