Zona-free hamster ovum penetration by human spermatozoa: influence of various sperm factors.

The present paper evaluates the influence of various technical factors when preparing human spermatozoa to be tested for their ability to penetrate zona-free hamster ova. Higher in vitro fertilization rates were obtained after sperm selection by "swim-up" migration, 4-h incubation, sperm dilution to a concentration of 2.5 X 10(6) spermatozoa/ml, and observation of the oocytes 8 h after insemination. The use of control samples was necessary because of wide intraindividual and interindividual variations in the results. Unless the result has been confirmed several times, it is impossible to conclude, from a negative test, that a human spermatozoon cannot penetrate a hamster oocyte.