[Under what conditions can further course research still be expected to produce new knowledge on endogenous...

Exhaustive follow-up studies of schizophrenia from Zürich, Bonn and Lausanne have produced strikingly similar results, despite considerable methodological differences. These 'classical' modes of differentiating the endogenous psychoses are critically analyzed. In contrast, the application of the operational research criteria recently developed by American authors results in a narrowing of the concept of schizophrenia and a proportional broadening of the cyclothymic disorders. Use of the Viennese research criteria, the definition of an 'axial syndrome' of schizophrenia, has the identical nosological effect. While the American diagnosis is phenomenological and essentially 'atheoretical', the Viennese view is based on the hypothesis of a core disorder. Further comparative polydiagnostic studies are called for in order to determine the relative value of these various research instruments.