Challenge test with oral m-CPP and placebo were performed in 12 healthy, young volunteers (6 male, 6 female) in a double-blind, placebo-controlled, cross-over study to assess possible gender differences in serotonergic responsivity. Women but not men showed significant prolactin and anxiety increase after administration of 0.25 mg/kg oral m-CPPP. Core temperature increased in both sexes compared to placebo. m-CPP induced significant physical symptoms only in men. Gender differences in serotonergic functions may have clinical significance with regard to differences in rates of some psychiatric disorders between the sexes.