Penetration of bovine cervical mucus (BCMP) by human spermatozoa has been reported to be a test that may aid in assessment of male fertility. We determined the predictive value of BCMP for conception in 127 infertile couples. Fresh semen and swim-up specimens were tested with the Penetrak assay. Out of 127 patients 16 (13%) achieved pregnancy with 6 months to 2 years of follow-up. In the 62 men with sperm counts of greater than 20 million/ml and motility of greater than 60%, 55 (89%) had adequate BCMP while adequate penetration was found in only eight of 24 (33%) with both sperm count and motility below these values (p less than 0.001). A normal BCMP did not predict pregnancy, and a reduced BCMP had no prognostic value in designating couples not likely to conceive. The comparison of penetration values for semen following swim-up suggests that this preparation may improve the correlation of BCMP with fertility. These results indicate that the semen parameters of sperm density and percent motility predicted spermatozoal performance in the BCMP assay, and that the assessment of BCMP did not predict the likelihood of pregnancy.