A vaginal lavage from a preferred female sexual partner (donor) with whom old (21-27 yr) rhesus males readily copulated or a distilled water lavage was applied to the perineum of non-preferred females (N = 8) with whom old males rarely copulated. The donor and recipients were ovariectomized and were treated with estradiol benzoate (EB) before being tested. Sexual performance of the males did not differ under the two conditions of testing, but the rate of sexual solicitation by the females was significantly higher when treated with the vaginal lavage. One month later the non-preferred females were again treated with EB and paired with the old males. In these tests the preferred female was present in a cage adjacent to and in view of the test pairs. Sexual behavior was not altered significantly, but whereas these males had never threatened or aggressed their partners in previous tests, there was a significant increase in the rate at which they threatened their partners and aggression occurred for the first time. When paired with the preferred female, males ejaculated in 100% of the tests and the average ejaculation latency was less than 2.5 minutes.