The purpose of the proposed studies is to investigate the role of estrogen on mood and behavior in normal healthy menstruating women. One goal is to investigate the mood-altering and behavioral effects of varying concentrations of estrogen, first as a result of normal physiological fluctuations that occur naturally across the menstrual cycle, and second as a result of exogenous administration of single doses of transdermal estrogen. The second goal is to investigate interactions between estrogen and a stimulant drug, d- amphetamine. This combination will be studied both during the course of the normal cycle, and after exogenous administration of both estrogen and amphetamine. It is hypothesized that estrogen will produce mood-enhancing effects, and that the effects of d- amphetamine will be greater in the presence of higher levels of estrogen. These interactions are expected because both estrogen and d-amphetamine enhance activity of the dopaminergic system in the brain.