sperm penetration assay (SPA), a test for the ability of spermatozoa to penetrate oocytes in vitro. Hamster oocytes that lack the zona pellucida are exposed to the spermatozoa in question. Such zona-free oocytes can undergo heterologous membrane fusion with the membranes of spermatozoa that have undergone the acrosome reaction. An assessment is then made of the proportion of oocytes that have been successfully penetrated.
