The interactions between actomyosin (AM) and sarcoplasmic proteins (SP) during heat denaturation were investigated using mixed solutions a tμ 0.6 and pH6.8. When mixed with AM, SP which should otherwise be precipitated, remained to a fairly large extent in solution, binding to AM in the temperature range between 35° and 50°C. On the other hand, at temperatures between 50° and 90°C, AM, which does not precipitate in simple solution, aggregated with SP to form precipitates. The amount of protein remaining in solution after heating for 15min at 90°C varied critically with the mixing ratio of AM to SP. At ratios higher than 6:4 no coagulation occurred, while at ratios lower than 2:8 all the proteins except for the “non coagulable” fraction of SP were precipitated. The limiting ratio for coagulation, however, tends to increase as the pH of the solution is lowered.