Duoperone is a neuroleptic agent. Duoperone blocked d-amphetamine lethality in mice under aggregated conditions when the pretreatment interval was between one hour and seven days. Conditioned avoidance responding in mice and cats was suppressed by duoperone in doses that did not impair escape behavior. Duoperone produced catalepsy in rats. The onset of this effect was delayed and the duration was prolonged when compared with that of chlorpromazine. It was a potent antiemetic agent in dogs, with a delayed onset and prolonged duration of action.