This report reviews a number of studies which support our current classification schema for affective disorders. This classification differentiates between an anxious-hyperactive type and an anergic-hypoactive type which are then further subdivided into primary and secondary affective disorders. While the motor and activity measurements are for the most part limited to patients suffering from primary affective disease, current studies under way indicate that secondary affective disorders may also have characteristic biologic changes. EEG sleep and motor activity parameters provide useful pointers for differential diagnosis and treatment while having the added advantage of diminishing the clinician's almost exclusive dependency on amnestic data and the psychological observations made on the patient's behavior.