In order to see whether the mamillary bodies participate in the control of female gonadotrophic function, 12 female rats in which the mamillary bodies were damaged by passing 0.3 ma direct cur-rent through stereotaxically implanted electrodes, 8 rats which received the same treatment except passage of current, and 9 normal rats were prepared. One month after the operation, all animals were sacrificed and their brain lesions checked histologically, their ovaries and uteri examined and weighed. The ovaries and uteri showed neither atrophic changes in any animal, nor significant differences in the weight among the 3 groups. Thus the results do not support the idea that the mamillary bo-dies are implicated in the control of female gonadotrophic function.