STUDIES upon the mechanism by which normal1men acclimatize to heat, carried out in our laboratory between 1943 and 1946, gave information which was responsible for the recognition of primary aldosteronism as a clinical entity. This included evidence that: In the process of heat adaptation an endogenous desoxycorticosterone-like steroid is produced in large amounts as reflected in decreasing concentrations of sodium in thermal sweat. Administered desoxycorticosterone produced the same effects. Increased steroidal activity of this type continued in the absence of evidence of increased activity of the adrenal cortex in other respects. The ability of the acclimatizing man to maneuver himself into a condition of positive sodium balance, despite large sweat volumes, was accomplished by an integrated response of the kidney and sweat glands with respect to salt conservation, and that this was mediated by increased activity of the endogenous desoxycorticosteronelike steroid. Renal escape from