In order to investigate the possible stimulating effect of danazol on fertility, a randomized clinical trial was performed on 40 women with unexplained infertility. Of these 40 women, 21 received 200 mg of danazol daily for 100 days and 19 received a placebo treatment during the same period. Serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, estrone, estradiol, progesterone, and testosterone were followed before, during, and after treatment. Danazol administration induced anovulation in all women, with prompt resumption of normal ovulatory function after discontinuation of the drug. No influence was seen on serum LH, FSH, and testosterone levels, but serum estrone, estradiol, and progesterone levels decreased significantly during treatment. Serum prolactin levels also decreased, but not significantly. No pregnancies occurred in the placebo group during a 6-month follow-up period. In the danazol group, five pregnancies occurred, of which two were ectopic and three went to term. The difference in pregnancy rate between both groups was statistically significant (P less than 0.05).