Orchidectomy in male rats leads to a) an increase in serum LH and FSH within 9 h; b) a decrease in serum testosterone to baseline levels by 30 min; c) an increase in serum progesterone (for 30 to 120 min), in the presence of the adrenals. If adrenalectomy is performed simultaneously with orchidectomy, the LH and FSH rises at 9 and 12 h are abolished, and the rises at 24 h are attenuated or abolished. By 48 h, the orchidectomized-adrenalectomized rat has achieved a rise in serum LH and FSH equal to that found in gonadectomy alone. Two hypotheses are offered to explain the abolition of the early gonadotrophin rises after combined orchidectomy-adrenalectomy treatment: a) the early responses are due to increased serum progesterone, on a background of decreased testosterone; b) the early responses are abolished because of the missing corticosterone, which either forces competition between pituitary secretion of ACTH and LH/FSH, or is necessary for rapid gonadotroph-secretory response. The differences and similarities between male and female rats, in the response of LH and FSH to gonadectomy, in the presence or absence of the adrenals, are discussed.