Seventeen patients with clomiphene-resistant hypothalamic anovulation were given tamoxifen 10 mg per day from cycle day 5 to 9 during two consecutive menstrual cycles. Not included were patients with hyperprolactinemia and PCOD. Treatment was monitored using measurement of follicle size by ultrasound and assessment of serum estradiol. Failure to ovulate persisted in 15 patients. Of the two patients who ovulated, one received hCG on day 16, and became pregnant. We were unable to demonstrate that clomiphene-resistant patients were likely to ovulate with tamoxifen. Forty-five patients with hypothalamic anovulation not previously treated were then given tamoxifen in the same dosage. This part of the study indicated that tamoxifen was successful in inducing ovulation in 84% of the cycles. There was marked improvement in cervical mucus in tamoxifen cycles as compared with clomiphene cycles. Tamoxifen was effective, and had some advantages compared with clomiphene in patients responding to both drugs. This preliminary study suggests that tamoxifen may be a useful addition to the treatment of ovulatory failure.