Old Long-Evans male rats (24–33 months of age) do show postcastration rise in serum LH but do not have postcastration LH rise in the pituitary both as expressed in content and concentration. The serum LH levels of intact and castrated rats of old age show a tendency of decrease, though not to the level of statistical significance. The pituitary FSH content and concentration of intact old rats are not different from those of young adults (3.5–5 months of age), whereas serum FSH level of intact old male rats is significantly higher than that of intact young adults. There is a postcastration rise in the pituitary FSH content as well as concentration and serum FSH level in both age-groups. The half-lives of endogenous and exogenous LH and FSH are not different between old male rats (24- to 31-month-old) and young adults (3- to 5-month-old). Blood testosterone levels begin to decline between the age of 12 and 18 months and remained low from 18 months of age on. These results indicate: (1) deficiencies in the LH regulatory mechanism in response to removal of gonadal steroids are easier to manifest than those of FSH control mechanism in old age in male rats; (2) the ability of clearing circulating LH and FSH of old male rats is not different from that of young adult males, if their molecular sizes are similar, and (3) high serum FSH level of old male rats is not due to prolonged half-life in the circulat