Kinetics of thermal inactivation of the rabbit liver microsomal cytochrome P-450 has been studied in the temperature range of 45-54 degrees C with increasing concentrations of glycerol. For all temperatures studied in the absence and presence of glycerol, thermal inactivation of cytochrome P-450 is characterized by two phases, the first being described by the first order rate constants. Glycerol markedly lowers the rate of thermal inactivation of cytochrome P-450 as well as the activation parameters delta H and delta S of the process of thermal destruction. There is a linear relationship between decreasing values of delta H, delta S and increasing glycerol concentrations in the medium.