Three genotypes of mice were shown to increase their intake of 3% sodium chloride (NaCl) following administration of fludrocortisone acetate (25 mg/kg), a synthetic steroid having strong mineralocorticoid/glucocorticoid activity. However, treatment with deoxycorticosterone acetate (DOCA) (10 mg/kg), a corticosteroid with predominantly mineralocorticoid activity, did not increase 3% NaCl consumption by the stock tested. In contrast, both fludrocortisone and DOCA have been shown to be effective activators of sodium appetite in rats. The essential importance of glucocorticoids in potentiating mineralocorticoid activation of sodium hunger in mice is suggested.