The rates of cell proliferation, total protein and heat shock protein turnover, and thermotolerance decay were determined in exponential-phase CHO cells. Following a mild heat treatment of 44 degrees C for 10 min, the rate of total protein turnover slightly exceeded the rate of cell proliferation. Heated cells doubled approximately every 16 h and labeled total protein turned over with a half-time of 14 h. The turnover rate of heat shock proteins (10-h half-time) somewhat exceeded the total protein turnover rate and was similar to the thermotolerance decay rate. These data indicate that the turnover of total and heat shock proteins and thermotolerance occurs as a result of both cell division-dependent and division-independent processes.