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A new method for the continuous measurement and recording of sweat rate has been developed. The sweat rate is determined by continuously measuring the change in resistance of a sensing element which, in turn, reflects the change in moisture content of a small volume of air. In operation, a chamber containing the element is fastened against the skin. Dry air is passed through the chamber at a sufficient rate to maintain an arbitrarily predetermined level of humidity within the chamber. A variation in sweat rate produces a change in the moisture content of the air and, consequently, a change in the resistance of the element. This change is nullified by means of a servo system which adjusts the flow of dry air so as to restore the original level of moisture. Thus, the air flow across the element at any time is a measure of the sweat rate.