Recent preclinical evidence indicates that ovarian hormones, such as estrogen and progesterone, may influence the behavioral effects of psychoactive drugs by interacting directly with neurotransmitter systems in the central nervous system. However, few studies have examined the effects of ovarian hormones on subjective or behavioral responses to psychoactive drugs in humans. In the present study, we assessed the subjective and physiological effects of d-amphetamine during the early and late follicular phases of the menstrual cycle. Nineteen healthy, regularly-cycling women participated in four sessions receiving doses of d-amphetamine (AMPH; 15 mg oral) or placebo during the early and late follicular phases of two menstrual cycles. During the early follicular phase levels of both estrogen and progesterone are low, whereas during the late follicular phase estrogen levels are higher while progesterone remains low. 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 menstrual cycle phase. However, subjects reported greater Unpleasant Stimulation after AMPH, and less Unpleasant Sedation, during the late follicular phase than during the early follicular phase. These results provide limited evidence that higher levels of estrogen during the late follicular phase alter the subjective effects of AMPH in normal, healthy women.