Proteins present in the eccrine sweat collected from the skin surface of male volunteers were studied. The protein content ranged from 0.154--0.774 g per liter. A total 2282 ml sweat was concentrated until a final protein content of 25 mg/ml was reached. Paper electrophoresis revealed 3 fractions migrating like alpha-, beta-, and gamma-globulins. Eight different proteins were demonstrated by immunoelectrophoretic analyses using rabbit antisera directed against human sweat proteins. Three of these proteins were identified as blood serum proteins. One of the remaining 5 proteins could be of epidermal origin; another one which occurs in comedones as well as in sweat seems to be eluted from the sebum film present on the skin surface.