Unfertilized oocytes from an in-vitro fertilization programme were stored in different saline solutions and then utilized in a zona binding assay (ZBA). The four saline solutions tested were identical with regard to the capacity of the zona to bind spermatozoa provided by healthy donors. Spermatozoa from 150 infertile patients were tested in the ZBA. The number of spermatozoa bound to the zona correlated positively with sperm concentration, the percentage sperm motility and the percentage of morphologically normal spermatozoa. The population was then divided into two groups according to the level of alpha-glucosidase activity, an epididymal marker. The average number of spermatozoa bound to the zona was diminished in the group with low alpha-glucosidase activity, even when considering strictly equivalent classes of sperm concentration, motility and morphology, respectively.