The purpose of the present work has been to study whether man, when he feels thermally comfortable, has a certain skin temperature and sweat secretion which is independent of his clothing, and how air temperature, mean radiant temperature and air velocity are combined in his environment. In other words, whether man at a given activity level prefers to have the same skin temperature and sweat secretion whether he is nude or clothed, whether he is exposed to a high or a low air velocity, or whether the air temperature is equal to or different from the mean radiant temperature.