Plasma levels of testosterone (T), luteinizing hormone (LH), and cortisol were measured in 10 adult male rhesus monkeys before and shortly after coitus. Mean levels of T and LH did not increase significantly after coitus or in control (no ejaculation) tests, but cortisol levels did in both cases. In 10 different males, no significant change was found in the plasma levels of T after electroejaculation; but in control tests (electric current withheld), the mean level of T was significantly lower at 80 and 140 min, but not at 50 min, after the test. According to present evidence, the effect of ejaculation on T levels differs in primate and nonprimate species. The effects on T levels produced by living with sexually receptive female rhesus monkeys may differ from those produced by intimate but brief contact with them.