The overall objective of the proposed research is to use the repeated-acquisition technique and a cumulative-dosing procedure to assess the effects of PCP in combination with other drugs on complex operant behavior in patas monkeys. In the first series of experiments, our specific aims are 1) to characterize the behavioral effects observed when PCP is administered in combination with another abused drug (cocaine, heroin, MDA, nicotine, methaqualone, alcohol, THC, or PPA) and 2) to determine whether the effects of the combination are predictable from the individual actions of the two drugs. In the second series of experiments, our specific aim is to test two potential PCP antagonists, namely, cyclazocine and chlorpromazine. With regard to methodology, the technique of repeated acquisition is important because it provides the means for studying drug effects on learning, defined as within-session error reduction, in individual subjects. This point is especially relevant to studying PCP's effects since there are often marked individual differences in the response to PCP. The cumulative-dosing technique is valuable because a dose-effect curve for a drug can be obtained in a single day. From a clinical point of view, it is important to study the effects of PCP in combination with other abused drugs because multiple drug use is widespread and such combinations can present a significant health hazard. The clinical significance of finding a specific PCP antagonist is self-evident. A specific antagonist would also be important theoretically in helping to unravel the neurochemical mechanism(s) underlying the behavioral effects of PCP.