PIP: A double-blind, prospective study during the fall of 1979 investigated the association between the menstrual cycles of 305 Brooklyn College undergraduates and their associates and the lunar cycles. All subjects were 19-35 years old and using neither OCs (oral contraceptives) nor the IUD. Approximately 1/3 of the subjects had lunar period cycles, i.e., a mean cycle length of 29.5 +/- l day. Almost 2/3 of the subjects started their October cycle in the light 1/2 of the lunar cycle, significantly more than would be expected by random distribution. The author concludes that there is a lunar influence on ovulation.