Testicular growth and secretory profiles of LH and testosterone were monitored in three bull calves implanted with oestradiol-17 beta and three bull calves implanted with oestradiol-17 beta and infused intravenously with LH releasing hormone (LH-RH; 500 ng/pulse per h, 30-s pulse) continuously between 34 and 42 weeks of age. Oestradiol-17 beta implants restricted testicular growth and spermatogenesis by interfering with the hypothalamo-pituitary-testicular endocrine axis. Initiation of pulsatile LH release by LH-RH pulse infusion was accompanied by a twofold increase in mean circulating levels of LH (3.4 v. 1.8 microgram/l) and a marked increase in serum testosterone (13.0 v. 0.4 microgram/l). Testicular diameter was enhanced significantly by week 4 of infusion and increased in a linear fashion up to and including week 8. Testicular weight (g) and total daily sperm production (X 10(9)) at 42 weeks of age were decreased in calves implanted with oestradiol-17 beta (105 +/- 14 (S.E.M.); 0.0) when compared with calves implanted with oestradiol-17 beta and infused with LH-RH (254 +/- 12; 1.2 +/- 0.3). Differences in testicular size and sperm production rates between LH-RH-infused and control bulls without implants (352 +/- 26; 3.3 +/- 0.9) were attributed to the 2-month delay between oestradiol-17 beta treatment and the initiation of LH-RH treatment. These results (1) confirm our earlier conclusion that oestradiol-17 beta can interfere with normal pubertal development in beef bulls and (2) provide additional support that pulsatile LH secretion is important for the initiation of testicular growth and spermatogenesis in pubertal bulls.