promazme, and d - amphetamine sulphate were administered to solitary adolescent rhesus monkeys whose behavior was observed, videotaped, and scored in a number of interaction of categories. Hallucinogens (LSD and DMT) could be distinguished from other drugs by the increased frequency of unusual behaviors such as spasms, stereotypy, and inappropriate behavior, and the decreased amount of exploration time. Hallucinogens also produced distinctive qualitative changes in behavior.