Mood fluctuations in women and men were studied both prospectively and retrospectively to determine whether cyclic changes occur over phases of the menstrual cycle, lunar cycle, and/or days of the week. The participants (1 5 women using oral contraceptives, 12 normally cycling women, and 15 men), who did not know the purpose of the study, recorded the pleasantness, arousal, and stability of their moods daily for 70 days (concurrent data). Later they recalled (retrospective data) their average mood for each day of the week and phase of the menstrual cycle (women only). The only evidence of mood fluctuation over the menstrual cycle in the concurrent reports was that normally cycling women reported more pleasant moods in the follicular and menstrual phase than did men and women on oral contraceptives. Women's moods fluctuated less over the menstrual cycle than over days of the week. Recollections of menstrual mood changes differed from actual changes: Women recalled more pleasant moods in the follicular phase and more unpleasant moods in the premenstrual and menstrual phases than they had reported concurrently. Bias also was evident in recollections of weekday mood fluctuations: Weekend highs were exaggerated and Monday blues were reported even though they were not reported concurrently. There was no evidence of mood fluctuations over the lunar cycle and the groups did not differ in mood stability. The retrospective reporting bias for both the This research is based on a thesis done by the first author under the co-direction of the second and third authors and submitted to the University of British Columbia in partial fulfillment of the requirements for the M.A. degree. Portions of this work were presented at the meeting of the Canadian Psychological Association, Halifax, June 1985.We gratefully acknowledge the helpful suggestions of Boris Gorzalka, Phillip Smith, Lawrence Walker, Janet Metcalfe, and James Russell.Requests for reprints should be sent to Jessica McFarlane, Psychology Department, 2136 West Mall, University of British Columbia, Vancouver, B.C., Canada V6T 1Y7.