The cortex of vertebrate adrenal glands secretes two major groups of hormones--glucocorticoids and mineralocorticoids. Glucocorticoids, which have an oxygen atom at carbon number 11, increase the rate of gluconeogenesis and increase the mobilization of lipids in mammals (Turner and Bagnara 1971). At the same time there is a decrease in protein synthesis. This latter effect may be homologous to a decrease in fibroblast growth in culture in the presence of certain corticosteroids (Ruhmann and Berliner 1965). The main function of mineralocorticoids, on the other hand, is to retain sodium ions. They have little or no gluconeogenic activity. Interestingly, however, these hormones also have been found to depress growth of mouse fibroblasts (Berliner and Ruhmann 1966). Although glucocorticoids and mineralocorticoids function through the mediation of DNA-dependent synthesis of RNA (Pan, Chin and Pai 1971) and several enzyme systems have been implicated in bringing about these responses (Talanti and Hopsu 1961, Fallon and Byrne 1967, and Turner and Bagnara 1971), the precise mechanism of action is still not well understood.