The effect of oral gestrinone, 2.5 mg twice weekly for 6 months, was studied in 11 women with mild or moderate endometriosis laparoscopically confirmed. The mean laparoscopic score decreased from 17.18 to 9.09 (P greater than 0.005). Painful symptoms were relieved in all patients within 2 months from start of therapy. Gonadotropins, prolactin (PRL) 17 beta-estradiol (17 beta-E2), estrone (E1), progesterone (P), androstenedione (A), and dehydroepiandrosterone sulfate (DHEA-S) remained in the follicular phase range. Total testosterone (TT) and sex hormone-binding globulin (SHBG) decreased, whereas free testosterone (FT) slightly increased. Metabolic studies showed a decrease of total triglycerides, very low-density lipoprotein (VLDL) triglycerides, and high-density lipoprotein (HDL) and VLDL cholesterol, parallel to the decrease of associated apoproteins. Low-density lipoprotein cholesterol and apoprotein B increased during therapy. The results suggest that gestrinone possesses antiestrogenic, androgenic, and progestigenic effects at therapeutic dosages both by acting on central and peripheral steroid receptors. For its efficacy and good tolerance, gestrinone may be considered an option for treating endometriosis.