The inconsistent findings of studies of physical and psychological changes throughout the menstrual cycle are reviewed in terms of three different forms of arousal - behavioural, autonomic, cortical. The review indicates that the premenstrual phase is characterized by increased levels of behavioural and of autonomic arousal. The nature of premenstrual changes in cortical arousal is unclear. It is suggested that differentiation and measurement of the various aspects of arousal throughout the cycle may lead to better understanding of the processes underlying the reported changes and of the practical implications of such information.