Vitamin [vit] E (.alpha.-tocopherol) is required for testicular function but its action on specific testicular cells has not yet been studied. Porcine Leydig cell cultures, in a hormone-supplemented medium, were used to study the effect of vit E on Leydig cells. The addition of vit E to the medium led to an increase in cell survival, lengthening the life span of the cultures from 3-4 days to more than a week. The Leydig cells maintained their lutropin/hCG [human chorionic gonadotropin] receptors and responsiveness throughout this period as evidenced by an increase in testosterone (T) and prostaglandin [PG] secretion. The hCG stimulated T levels were synergistically increased in the presence of vitamin E, while basal levels of T secretion were not changed. Other secretory products of Leydig cells are PGE2 and PGF2.alpha.. The addition of vit E inhibited both the basal PG levels and the stimulated levels by 90%. Maximal effects on all these parameters were seen at 10 ng/ml vit E. Vit E obviously plays a critical role in maintaining porcine Leydig cells in primary cultures beyond the first 3 days. This vitamin seems to be involved both in steroidogenesis and in PG production in the Leydig cells. The exact mechanism of the action of vit E on these 2 biosynthetic pathways remains to be determined.