1. Amino acid nitrogen in sweat varied widely between 10.2 and 1.1 mg. per cent and inversely with the rate of secretion.2. In the sweats collected simultaneously from extremities and trunk, the former was much higher in its concentration of amino acid nitrogen.3. In human skin, values of free amino acid nitrogen of 10.0 to 13.5mg. per cent with a mean level of 12.2mg. per cent were found in chest and abdomen. Much higher values, however, were obtainable in other various regions of the body. In guinea pig skin it ranged from 65.9 to 45.1 mg. per cent (36.1mg. per cent on an average), these were about the same as in solid organs.4. The following 16 amino acids were observed in sweat on paper chromatogram: serine, threonine, valine, leucine, isoleucine, lysine, glutamic acid, aspartic acid, proline, phenylalanine, tyrosine, tryptophan, histidine, arginine, methionine, and cystine.5. The reason why glycine, alanine, and glutamine, despite of their presence in skin, were not found in sweat was discussed.