The present study examined the effects of a specific D2 dopamine receptor agonist, quinelorane (LY163502), on male sexual responding of rhesus monkeys. The effects of quinelorane were assessed by observing the behavioral responses of male rhesus monkeys to a sexually receptive female monkey that they could see, hear, and smell, but not physically contact. Quinelorane (IM) treatment produced dose-dependent effects on male sexual responding. Penile erections and masturbation were markedly facilitated following treatment with either 2.5 or 5 micrograms/kg quinelorane. Higher doses of quinelorane (10 and 25 micrograms/kg) generally did not further augment sexual responding, but rather resulted in a return in sexual responding to control vehicle levels. Quinelorane had a biphasic effect on yawning behavior of the monkeys with low doses (2.5 and 5 micrograms/kg) facilitating yawning and high doses (25 micrograms/kg) inhibiting yawning. Quinelorane in the dose-range (1-25 micrograms/kg) being evaluated did not reliably influence stereotypic behavior. In order to determine whether quinelorane acts centrally or peripherally to stimulate male sexual behavior, the ability of the peripherally active dopamine antagonist, domperidone, and the centrally active dopamine antagonist, haloperidol, to block the facilitation of sexual behavior produced by quinelorane treatment was examined. Administration of domperidone (50-200 micrograms/kg) failed to block quinelorane's effects on sexual behavior, whereas treatment with haloperidol (5-20 micrograms/kg) prevented quinelorane from stimulating male sexual responding. These experiments provide further evidence that dopaminergic mechanisms may play a role in the regulation of male sexual behavior of rhesus monkeys and, in particular, demonstrate the sexual stimulant properties of agents that provide central stimulation to D2 dopamine receptor sites.