One hundred seventy-eight ejaculates obtained from infertility patients were evaluated by routine semen analysis and by a bovine cervical mucus penetration test (BCMPT). A significant correlation (p less than 0.01) was observed between mucus penetration and both sperm count (r = 0.349) and sperm motility (r = 0.394). One hundred fifty-two of 178 patients (85%) had normal sperm counts (greater than 20 x 10(6)/ml). Of these patients, 68% had good (greater than 30 mm), 26% had questionable (21-30 mm), and 7% had abnormal (less than 20 mm) penetration values. One hundred sixty-one of 178 patients (90%) had normal sperm motilities (greater than 40%). Of these patients, 71% had good, 25% had questionable, and 4% had abnormal penetration values. Conversely, 46% and 18% of patients with abnormal sperm count and motility, respectively, had normal penetration values (greater than 30 mm). A significant relationship (p less than 0.05) was observed between the BCMPT and pregnancy problems not apparent by semen analysis data, and may prove to be a useful adjunct to the use of routine semen analysis in evaluating male fertility.