Two groups of young rhesus monkeys were subjected to repetitive peer separations, a procedure that has been shown to produce depressivelike reactions in infant monkeys. Midway through the procedure one group was treated with the antidepressant imipramine hydrochloride, the other with a saline placebo. In comparison with placebo treatment, the imipramine treatment yielded significant behavioral improvement in a form and with a time course similar to that seen when the drug is given clinically to human depressives. We discuss the implications of the findings.