A telemetered movement recording system and nursing ratings of behavior were utilized to assess spontaneous motor activity and symptom intensity of 15 patients with affective illness before and during lithium carbonate treatment. Prior to treatment, patients rated hyperactive-elated, angry, and agitated had more motor activity, and patients rated anergic and retarded had less motor activity. Lithium carbonate treatment was not associated with any uniform change in motor activity for all patients; however, patients with a decrease during treatment in thought disorder, motor agitation, and hyperactivity-elation had a decrease in motor activity, and patients who had a decrease in depressed mood, anergia, motor retardation, and social withdrawal had an increase in motor activity. The decrease in activity of manic patients, except for the 11 p.m. to 3 a.m. period of apparent sleep, appeared to occur fairly uniformly throughout the 24-hour period, but the increase in activity of the depressed patients occurred mostly during the daytime. The data indicate that lithium does not exert a strong and consistent direct effect on spontaneous motor movement, and that when changes in movement do occur, they relate to changes in clinical states.