The morphological changes of uterine and oviductal mucosae after successive administrations of charcoal-treated porcine follicular fluid (CTPFF) in rabbits were examined. In Experiment 1, mucus secretion in uteri of four does which were injected with 4 ml of CTPFF 10 times at 12-hour-intervals was not so active as that of controls (three does). In Experiment 2, thirteen does were injected with 4ml of CTPFF in the same manner as in Experiment l, and were divided into 4 groups according to the number of hours --- 0 (5 does, group 0F), 12 (4 does, group 12), 36 (2 does, group 36) and 96 (2 does, group 96) hours, respectively --- from the final injection of CTPFF to human chorionic gonadotropin injection. The proliferation of uterine mucosa in does of groups 0F, 36 and 96 was repressed in comparison with that in the control group. The numbers of mitoses in the glandular epithelium of groups 12, 36 and 96 were significantly lower (p <0.01) than those of groups 0F and 0S. The ratio of ciliated cells in the mucosal surface epithelium of group 0F was significantly higher (p < 0.01) than in groups 0S and 12. In Experiments 1 and 2, swelling of epithelia1 cells and production and release of mucus in the ampulla were slightly repressed in does of treatment groups. It seems that administration of CTPFF represses the proliferation of endometrium indirectly through the ovary, but the effect of CTPFF on the oviduct is slight.