In this paper 31 patients with a diagnosis of manic depressive, manic are matched for age, sex and socioeconomic status with 31 patients with a diagnosis of manic depressive, depressed. The study shows that hospitalized manics contain a higher percentage of men than hospitalized depressives and the manics are hospitalized at an earlier age. It is also noted that the first symptoms are seen at an earlier age. There were no significant differences in the family histories of manics and depressives. Turning to the clinical picture of mania, cuphoria, overactivity and push of speech were seen in almost all patients studied. Objective confusion was seen in 18 of the 31 (58 per cent) patients. Eighteen of 24 patients (58 per cent), in whom information about depressive symptoms was recorded, reported a depression immediately preceding the onset of the mania. Special attention was given to those patients who exhibited schizophrenic symptomatology in their index admission. Seven patients with passivity feelings were personally interviewed approximately 2 years after their index admission. It was found that in none had classical schizophrenia with deterioration developed. Their cases histories are presented.