Fludrocortisone acetate (Florinef) is a synthetic steroid with a potent mineralocorticoid action, and used for treatment of Addison's disease and salt losing form of congenital adrenal hyperplasia. It is also used for severe hypotension to restore adequate plasma volume. Caution is necessary for possible side effects of hypernatremia, hypokalemia, hyperglycemia and congestive heart failure when used chronically. A synthetic steroid which selectively binds and activates renal MR-LBD but not GR, or non-epithelial MR, although not found at present, may be a promising mineralocorticoids to be used in the above disorders.