1. The comparison of the women taking oral contraceptives with the women not taking oral contraceptives showed no qualitative or significant quantitative differences in the excretion of amino acids in thermal sweat collected from the total body surface. 2. The comparison of the trained women with the untrained women neither revealed qualitative or significant quantitative differences in the excretion of amino acids in thermal sweat collected from the total body surface. 3. As compared to the trained men, untrained men excreted in thermal sweat collected from the total body surface significantly more alanine, arginine, citrulline, cystine, glycine, histidine, isoleucine, leucine, lysine, phenylalanine, serine, threonine, tyrosine, and valine. 4. The sex-specific comparison of the amino acid excretion in sweat showed that men had a significantly increased excretion of cystine, histidine, leucine, and taurine. Proline was detected only in the sweat of women. 5. The quantitative results obtained for the amino acid excretions during 12 min of sauna bathing suggest that persons exposed to hard, physical activity and/or high environmental temperatures have quite equal amino acid losses in sweat and in 24 h urine.