1. As a prerequisite for psychopharmacological studies in subgroups of psychiatric patients two approaches will be described: a. A multiaxial classification system for affective disorders (MULTI-CLAD). b. Studies of ABO- and HLA-systems in patients with affective disorders. HLA: In 107 manic-melancholic patients selected according to the very strict MULTI-CLAD criteria confirmatory evidence was obtained that there is a positive association between affective disorders and HLA-Bw 16; the results were also strongly suggestive of a positive association between HLA-7 and such disorders. ABO: In sixty-six manic-melancholic patients selected along the same criteria, the differences between all patients combined versus controls were not significant, but a significantly higher percentage of bipolar patients (70%) than of unipolar patients (22%) had blood group O, while a significantly higher percentage of unipolar patients (65%) than of bipolar patients (23%) had blood group A. 2. The findings are in the process of further study involving some 300 patients from the Psychochemistry out-patient-clinic. The purpose is to see whether less selected groups of patients with affective disorders show less marked profiles for ABO and HLA, as this will have importance for the selection of subgroups of patients for psychopharmacological studies.