Sixty-nine infertile women with a midluteal serum progesterone level of 4 to 14 ng/ml were treated with a graduated dosage schedule of clomiphene citrate until the progesterone level on day 21 was greater than 20 ng/ml. Thirty-one pregnancies occurred, 58% during the first adequate treatment cycle and 19% during the second cycle. The abortion rate was 23%. After 6 adequate treatment cycles, laparoscopic evaluation was performed on 28 of 39 patients who did not conceive. Pathology was noted in 57%. Seven of 17 patients with intraperitoneal causes of infertility conceived after alternative therapy. The corrected pregnancy rate was 60%. Results of this study suggest that low luteal phase progesterone levels may compromise fertility and that clomiphene citrate enhances pregnancy rates.