The functional competence of human spermatozoa recovered after vasectomy.

Progressively motile spermatozoa were present in 42/47 (89%) of post-vasectomy specimens, and in 16 of 24 samples (66%) demonstrable fertilizing potential could be detected in the zona-free hamster egg assay. The mean +/- s.e.m. post-vasectomy penetration rate of 20.6 +/- 6.0% was, however, significantly lower (P less than 0.001) than the pre-vasectomy value of 49.7 +/- 6.4%. After vasectomy the concentration of motile spermatozoa in the ejaculates declined in a manner that was significantly correlated with the post-operative time interval. The spermatozoa also lost their potential for fertilization, although functionally competent spermatozoa were still being recovered from ejaculates produced 8 days after vasectomy. These results emphasize the ability of human spermatozoa to retain some residual fertilizing potential when stored at core body temperature in sites distal to the epididymis, and suggest a role for functional tests in the management of the vasectomized male.