Characteristics of follicular development and hormonal patterns were evaluated in 17 women with minimal endometriosis and 11 with unexplained infertility. The controls were 7 women with male factor infertility and 8 who conceived during an investigational cycle. Women with minimal endometriosis had more and smaller follicles at luteinizing hormone (LH) surge, lower preovulatory estradiol (E2), and lower E2 at LH surge. Women with unexplained infertility had lower LH surges and a trend to a shorter follicular phase. Occult ovulatory dysfunction and may contribute to infertility in women with minimal endometriosis or unexplained infertility.