Acid and heat-resistant proteins (thermosoluble proteins) were isolated from urine after exercise. These proteins were divided by starch block electrophoresis into 5 subfractions with 30 sections. Donaggio titer and protein measurement were done for each section, and the relationship between thermosoluble proteins and Donaggio specific activity (Donaggio titer/total protein concentration) was investigated. The results were: 1) The Donaggio specific activity of the 5 subfractions with 30 sections was maximum in the alb. ~α1-glob. region. It increased after treatment by heating at 100℃ for 10 minutes and acidification to pH 5. 2) A significant rise in the protein concentration of urine after exercise was observed in the alb. and αl-glob. regions. 3) The Donaggio specific activity of serum was higher than urine for equivalent protein concentrations. 4) Thermosoluble proteins were identified as Donaggio substances. The Donaggio specific activity of proteins was in the order of alb.,>α1-glob.>α2-glob.≫β-glob., γ-glob.. 5) The most important proteins contributing to the Donaggio titer were thought to be alb. and αl-AG, judging from correlation coefficients between Donaggio titers and protein measurement. The differences between alb. and αl-AG, before and after treatment were not statistically significant. Measurement of thermosoluble proteins in urine may be a useful method of determining the magnitude of the load imposed by physical exercise upon an individual.