1. Circulating immuno-reactive-luteinising hormone (LH) and follicle stimulating hormone (FSH) were measured between hatching and either 17 or 30 weeks of age in turkeys. 2. In one experiment both sexes were reared together. The pattern of changes in gonadotrophin concentration with age consisted of high LH concentrations at 3 to 8 and 16 to 19 weeks old and FSH peaks between weeks 3 and 10 and at weeks 18 and 19. 3. In two separate experiments male and female birds were reared separately for 17 weeks. In these turkeys the LH concentration was high for 3 weeks following hatching and also after 10 weeks, while FSH was elevated at weeks 10 and 15 in females and at weeks 7 and 13 in males. 4. There were lower plasma LH concentrations in turkeys which had received testosterone implants while the FSH concentration was elevated. 5. Pinealectomy in female turkeys led to increased FSH concentrations at 2 weeks but depressed FSH concentrations thereafter.