Short and long term effects of sulpirid on the sleep EEG in humans were investigated in 8 patients aged 20-68 years (average 40.4) suffering from autonomic instability. In each patient seven polygraphic night sleep recording were performed. After an adaption night and two nights without medication each subject got 200-400 mg sulpirid i.m. for two days and then 300-600 mg orally for a three-week period. In both groups the short-term application of sulpirid caused a reduction of waking periods and a slight decrease of stage 3, while stage 2 was increased. In psychotic patients the long-term orally administered substance was followed by an increase of deep synchronous sleep (stage 4). As this alteration of sleep couldn't be revealed in the control group, we consider this finding as a result of the improvement of psychosis. In the patient group the amount of REM sleep was augmented during the short-term application as well as during the long-term application, where, as in the control group the amount of REM sleep decreased when sulpirid was given orally for three weeks. This result is discussed in comparison with the properties of the tricyclic antidepressant drugs and monoamine oxidase inhibitors and the clinical effects of sulpiride.