Little is known about the interactions between ovarian hormones and responses to psychoactive drugs in humans. Preclinical studies suggest that ovarian hormones such as estrogen and progesterone have direct and indirect central nervous system actions and that these hormones can influence behavioral responses to psychoactive drugs. In the present study, we assessed the subjective and physiological effects of d-amphetamine (AMPH; 10 mg p.o.) after pretreatment with estradiol. Two groups of healthy, regularly cycling women participated in two sessions scheduled during the early follicular phases of two menstrual cycles. One group received estradiol patches (Estraderm TTS; 0.8 mg) which elevated plasma estradiol levels to approximately 750 pg/ml on both sessions; the other group received placebo patches on both sessions. Both groups received AMPH (10.0 mg) and placebo in a randomized and counterbalanced order on the two sessions. Dependent measures included self-report questionnaires, physiological measures, and plasma hormone levels. Most of the subjective and physiological effects of AMPH were not affected by acute estradiol treatment. Nevertheless, estradiol pretreatment increased the magnitude of the effects of AMPH on subjective ratings of ‘pleasant stimulation’ and decreased ratings of ‘want more’. Also, estradiol produced some subjective effects when administered alone: It increased subjective ratings of ‘feel drug’, ‘energy and intellectual efficiency’, and ‘pleasant stimulation’. These results provide limited evidence that the stimulating effects of AMPH are increased by acute estradiol pretreatment.