The effects of American ginseng (Panax quinquefolium) on male rat copulatory behavior were investigated. Adult Sprague-Dawley rats were administered either 10, 50 or 100 mg/kg of Panax quinquefolium or a sesame oil vehicle per os (p.o.) for 28 days and copulatory behavior parameters were measured. Ginseng-treated male rats demonstrated a significant decrease in mount, intromission and ejaculation latencies compared to vehicle controls. Hormone analyses revealed no difference in plasma luteinizing hormone or testosterone levels between ginseng- and vehicle-treated animals; however, plasma prolactin levels were significantly reduced by all doses of ginseng tested. When male rats were treated with the 100 mg/kg dose of ginseng for 1, 14 or 28 days, mount and intromission latencies were significantly reduced at 14 and 28 days of daily ginseng treatment, whereas ejaculation latency was significantly reduced after 1 day of ginseng treatment when compared to vehicle controls. Plasma prolactin levels were also significantly decreased after 14 and 28 days of daily ginseng administration. There were no differences in body weight or in testes, seminal vesicle, anterior pituitary or spleen weights between ginseng- and vehicle-treated rats. These results demonstrate that P. quinquefolium significantly facilitates male copulatory behavior. The reduction in plasma prolactin levels suggests that ginseng-induced alterations in dopaminergic neurotransmission may play a role in the ability of P. quinquefolium to stimulate copulatory behavior in the male rat.