The ability to distinguish separate types of disorder among patients who seem at first sight to have similar symptoms has been a powerful factor in the progress of medicine. It is for this reason that the attempt to distinguish different varieties of depressive illness is important. In Britain recent studies have been concerned with the presence (as rated by the examining physician) of various symptoms and signs which from clinical experience have been thought likely to distinguish a neurotic from a psychotic type of depression. The investigators agree on the presence of these two types but disagree on the nature of the distinction, one school holding that there are two largely distinct types of illness and the other that the types merely represent the opposite ends of a continuum. The holders of the latter view accept that there may well be distinct types of depressive illness, but maintain that, if so, they cannot be distinguished by present methods of clinical examination. The divergence of view has been attributed by Kendell (1968) to sampling differences and to the subjective bias of raters, and by Eysenck (1970) to disagreement on whether the two types of depressive illness are of a categorical nature (i.e. specific disease entities) or of a dimensional nature (i.e. each has a graded distribution in a population of depressed patients).