In a previous study (Kornetsky, Humphries and Evarts, 1957) it was found that the impairment of a variety of psychological processes caused by 200 mg. of chlorpromazine was not significantly less than the impairment produced by 200 mg. of secobarbital. It was also shown that the effects of drugs on psychological performance in man are related not only to the specific pharmacological activity of the drug, but also to the specific reactivity of the subject. It appeared that there was something unique to the individual which accounted for a significant portion of the effect of a drug. The present study was designed to extend these observations by reducing the number of drugs tested (in the previous study four drugs were used) and increasing the number of times a subject received each drug. It was hoped that this would give a better estimate of the effect of a specific dose of a specific drug and thus decrease the error of measurement and increase the reliability of the correlation between drugs.