Effects of the gossypol on endometriosis in 12 cases of control were observed. The results showed that the gossypol administered orally was effective in endometriosis patients. The basal body temperature changed from biophase to monophase. Dysmenorrhea disappeared in 11/12 patients. Amenorrhea occurred in 10/12 patients and the ovarian endometrial cyst was shrinkable. Serum progesterone and estradiol were decreased after gossypol administration, but follicle-stimulating hormone and luteinizing hormone were increased evidently. Histochemical and cytochemical observations revealed that the activity of acid phosphate (ACP), nonspecific esterase (NSE) and alkaline phosphate (AKP) in both aberrant uterine endometrium and uterine endometrium in situ were decreased evidently. The above results suggest that the satisfactory therapeutic effect of gossypol on endometriosis may be due to not only the indirect but also the direct action on uterine endometrium.