The induction of infertility in males of several species through epididymal interference is more difficult to achieve by reduction of the amounts of epididymal secretions (eg alpha-glucosidase, L-carnitine) or immunological interference with secreted proteins (eg D/E, P34H, P26h) than by direct actions of drugs on sperm function (eg inhibition of glyceraldehyde 3-phosphate dehydrogenase by chloro-compounds). The latter approach holds promise for mankind as human sperm are susceptible to glycolytic inhibition. Future contraceptive developments may arise from production of targeted inhibitors, research on the displacement of sperm proteins in the epididymis and interference with sperm plasma membrane ion channels.