Recently one of us1 studied and reported on the content of reducing substances in sweat. One of these, which has been much studied recently, is vitamin C (cevitamic acid). We are reporting on its quantitative presence in sweat. Its physiologic action is not yet definitely established, although by virtue of its enol group it is supposed to play a rôle as a redox system and catalytic agent. Vitamin C has been found in the urine as a constant constituent, the amount excreted being dependent among other factors on the amount available in the body at the time. So far as we have been able to learn from a fairly thorough study of the literature, no one has yet reported on the presence of vitamin C in sweat. Since the composition of sweat approximates in many respects that of urine, one would expect vitamin C to occur in