In an attempt to demonstrate a valid boundary between schizophrenia and the affective psychoses, discriminant function analyses have been carried out with history, mental state and follow-up data in two populations of patients. A bimodal distribution of discriminant scores was obtained in one of them (a general psychotic sample of 128 patients), using a discriminant function derived from the same sample; but when the function was applied to the second population (a schizoaffective sample of 106 patients) the distribution was ambiguous. Functions derived from the schizoaffective sample produced highly skewed distributions of discriminant scores in the general psychotic sample. Kraepelin's hypothesis that the functional psychoses consist of two distinct disease entities receives some support from our findings, but there is still no compelling evidence that the universe of psychotic patients falls naturally into these two groups.