Gonadotrophin secretion by the pituitary was tested by i.v. injections of synthetic LH and FSH releasing hormone (LHRH) in five normal women between day 21 and day 25 of the luteal phase of the cycle, in twelve women receiving contraception with i.m. injection of medroxyprogesterone acetate and in eight women taking combined oral contraceptives of different varieties. Treatment with oral contraceptives led to a decrease or even to complete suppression of the response and possibly the reserve capacity of both LH and FSH secretions. Treatment with medroxyprogesterone acetate for several years lowered basal serum LH and FSH as did oral contraceptives but had much less effect on the responses to LRH. In long-term steroid contraception, progestogens alone seem to exert much less deleterious effect on gonadotrophin function than when used in combination with an oestrogen.