Paired male and female rats of the same age were studied in terms of their in vitro adrenal incubation with 3H-pregnenolone. The labeled products were isolated and measured. It was found that, comparatively, the formation of corticosterone, androstenedione and dehydroepiandrosterone was higher in the female; testosterone was formed more in the male, while 11-betahydroxyandrostenedione production was variable. The ratio of each individual C-19 steroid to corticosterone was higher in the male, and the androstenedione: testosterone ratio was always higher in the female.