The effect of temperature studies on polyphenol oxidase immobilized on glass beads were carried out in organic solvents. The optimum temperature for catalysis depended on the solvent and varied in a range from 26°C for dichloromethane to 50°C for toluene, benzene and 1,1,1-trichloroethane. Optimum temperature and activation energy were independent of the water content of the system whereas the inactivation energies decreased as the water content of the system was decreased. The enzyme was stable in toluene up to 50°C although residual activity depended on the water content of the system. Thermoinactivation of polyphenol oxidase in toluene gave an activation energy for enzyme decay of 111.5 kcal mol−1 which is consistent with a conformational process. Among the agents employed to protect the enzyme against thermal denaturation 1 % (w/v) short-chain polyols added to the buffer and 0.5 mmol dm−3p-nitrophenol added to toluene more than doubled the half-life of the enzyme.