In an attempt to mimic the events surrounding the natural onset of puberty in the male rat, animals were castrated and implanted with Silastic capsules filled with testosterone (T). Capsule size was adjusted to maintain serum-luteinizing hormone (LH) at sham-castrated values. To these animals implanted with T capsules, androstenedione (delta 4), 5 alpha-androstane-17 beta-ol-3-one (DHT), 5 alpha-androstane-3 alpha-17 beta-diol (3 alpha-OL) or T were administered by subcutaneous injections (40 micrograms/100 g body weight). 12 h later, the animals received an intravenous injection of 50 ng LH-RH. Pre- and post-LH-RH injection blood samples were assayed for serum content of LH and follicle-stimulating hormone (FSH) by radioimmunoassay. Compared to sham animals, prepubertal males showed a potentiation in the LH response with testosterone alone. This effect was not prevented by delta 4; DHT or 3 alpha-OL injection returned the LH response to that of sham-operated animals. No such effects of androgens were present in pubertal or postpubertal rats. There was no effect on the FSH response in any age group. Different groups of animals received 3 doses of 10 ng LH-RH or saline prior to a single 50 ng LH-RH injection. Pubertal and postpubertal males showed a self-priming effect of LH-RH on the LH response. This effect was not present in prepubertal rats nor in any group of animals that had been castrated, regardless of whether or not T replacement was performed. The results indicate that complex alterations in pituitary function take place during the sexual maturation of the male rat. These changes may be inherent in the pituitary and/or related to variation in testicular androgen secretion.