The purpose of Medical Hypotheses is to provide a forum for the presentation and criticism of ideas in medicine and the related biomedical sciences. Most biomedical journals will publish ideas only in papers which also report observations. As the best scientists have repeatedly emphasized, this gives a misleading impression of the process of discovery. The ideas usually come first and they determine what observations should and will be made. Although fully acknowledged in other sciences, this central role of ideas in scientific progress is only now beginning to be widely recognized in medicine. Ideas occur to many people not in a position to test them experimentally. Ideas frequently require much fuller exposition than is allowed in the discussion section of an experimental paper. Ideas should be open to comment by scientists who have not done experimental work in the field. Medical Hypotheses will publish ideas or criticisms of ideas from any person, irrespective of whether any experimental testing of the ideas has been performed by the writer. Medical Hypotheses will also publish letters which comment on articles in the journal. Medical Hypotheses is the only journal fully devoted to the publication of ideas in the biomedical sciences. The justification for its existence is discussed in the editorial printed at the beginning of the first issue (January-February, 1975). If you feel that the aims of Medical Hypotheses are important and worthwhile, please encourage your library to subscribe to it.