Abstract

PIP: Zona-free hamster oocytes were used to evaluate the entry of human spermatozoa into the oocytes. Suspensions of spermatozoa, free of seminal plasma, were preincubated for varying periods in a modified Tyrode's solution under mineral oil. Zona-free hamster oocytes were prepared and added to the sperm suspension for further incubation. At the end of the incubation period, groups of eggs were examined with both the phase-contrast and electron microscopes. A positive result was recorded when decondensation of the human sperm head was observed within the hamster oocyte. The highest rate of sperm entry took place after 3 hours of incubation. Polyspermy was occasionally seen. Photographic reproductions illustrate microscopic findings. Sperm of 31 of the 41 (76%) normal individuals gave a positive test but only 13 of 38 (34%) of suspected infertile patients did so. 1-hour preincubations were adequate to render spermatozoa capable of fertilization. This bioassay may be of value in investigations of male infertility and in assessment of the fertile condition of human spermatozoa when male contraceptives are to be tested.