1. An ambulatory activity monitor with solid-state memory was employed to obtain 24-hour activity data in 29 neuroleptic-treated hospitalized patients and 9 normal controls. 2. The activity monitor is a piezoelectric device which was strapped to the non-dominant ankle. Activity was recorded in 5-minute epochs throughout the 24-hour period. 3. In contrast to patients with mania (N = 15) and schizophrenia (N = 4), depressed patients (N = 9) had higher clinical ratings of akathisia and lower levels of daytime activity. 4. Manic and depressed patients showed a delay of peak activity (= acrophase). 5. Quantifiable alterations in rest-activity rhythms may occur in neuroleptic-induced akathisia but measurement of activity may be complicated by the patient's psychiatric disorder.