For prospective longitudinal confirmation of menstrually related mood changes, the authors selected a 100-mm visual analogue scale for twice-daily self-rating of mood. The advantages of this method are simplicity; increased compliance; ease of graphic presentation, allowing evaluation of severity and relationship to menstruation; and greater uniformity among studies of menstrually related syndromes. In a preliminary application of this measure to 20 women with self-diagnosed premenstrual syndrome, eight (40%) had a mean depression rating during the week before menstruation that was 30% higher than during the week after cessation of menstruation.