The effects of reserpine, chlorpromazine, phenidylate, amphetamine and meprobamate have been evaluated by highly quantitative spontaneous activity testing coupled with visual observation of rhesus monkeys. Normal monkeys and monkeys with inherent or induced locomotor hyperactivity were used. Reserpine and chlorpromazine produced a marked reduction in all activity when administered in quantities significantly smaller than those required to produce ‘taming.’ Phenidylate and amphetamine had a rather selective effect in drastically reducing the stereotyped pacing of the hyperactive animals. Meprobamate had no effect on the amount of spontaneous activity in any of the animals until dosages were employed which produced locomotor incoordination. No drug has been found to increase the amount of spontaneous locomotion in the monkey.