Forty-five male Ss divided into 3 groups, copulated either with "fresh" or "used" females introduced immediately after each ejaculation or with the "same" female lifted out and returned to them. Each group was further subdivided according to whether a fresh, used, or same female was provided after an exhaustion criterion of 45 min. was reached. The results indicated that changing partners before exhaustion had little effect on the response parameters relevant to mating. After exhaustion, fresh and used females rearoused activity and elicited 1-3 ejaculations.