Subcutaneous administration of d-amphetamine at various doses (1.25, 2.5, and 5 mg/kg) decreased plasma luteinizing-hormone levels in ovariectomized rats primed with estradiol and injected with progesterone. In these animals prolactin levels decreased after injection of 0.6 and 1.25 mg/kg of d-amphetamine. No significant hormone modifications were detected in oavariectomized and ovariectomized estradiol-primed rats after injection of 2.5 mg/kg of d-amphetamine. Fenfluramine at doses of 25 mg/kg induced decreases of plasma LH and prolactin levels in ovariectomized estradiol- and progesterone-treated rats. A low dose of fenfluramine, 2.5 mg/kg, had no effect. It is concluded that d-amphetamine and fenfluramine are able to alter the facilitatory actions of progesterone on luteinizing hormone and prolactin release in ovariectomized estradiol-primed rats.