 Twenty men with infertility, aged 21 - 60, due to azoospermia no apparent sperm in the ejaculate on two separate occasions will be enrolled in a single-arm pilot trial of daily oral therapy of 20 mg twice daily of 13-cis retinoic acid for 32 weeks. The impact of treatment on the appearance of sperm in the ejaculate will be determined by monthly semen analyses. 