Heart rate data as produced by the subjects under investigation both in resting conditions and taken as total means per trial initially showed a trend towards ergotropic, clearly tachycardiac behavior; with the onset of thymoleptic drug therapy, there followed a further increase in heart rate, frequencies remaining more or less stationary on this level during the 26-day period observed by us. We found differences between morning and evening data of session A with 50 % of subjects, 25 % showing higher frequencies in their morning data, the reverse applying to a further 25 %. The remaining 50 % did not show any differences worth mentioning. At the end of the investigation period, the relation changed in favor of an increase in heart rate in the evening with 50 % of subjects, whereas only 12.5 % showed increased heart rate jn the morning; 37.5 % did not show significant differences. We could not demonstrate these results to be related to diurnal variation, degree of depression or course of the disease.