The classification and nature of psychoses with both schizophrenic and manic-depressive symptoms is still highly controversial. The original view based on the Kraepelinian dichotomy of endogenous psychoses was that the “mixed” or “schizo-affective” psychoses were mixed also in a genetic sense. This would mean that some individuals inherit both schizophrenic and manic-depressive Anlage. This view has not been confirmed. One alternative is that proposed by Kleist and Leonhard, namely, that atypical forms of endogenous psychoses exist, which are genetically independent of both schizophrenia and manic-depressive psychosis. It seems, however, that Leonhard's concept has attracted little attention. Slater (1953) stated that Leonhard's work was “most interesting”, but hardly mentions it in his text-book of psychiatry (Mayer-Gross, Slater and Roth, 1960). An account of Leonhard's views on schizophrenia has however, been given by Fish (1958).