Stability performance of the acid protease of Cynara cardunculus L. in biphasic systems containing ethyl acetate, n-hexane or isooctane was investigated and compared with that of pepsin. Activity retention was higher in the system containing n-hexane. In this system 100% retention was observed up to 144 hours. Pre-saturation of phases was found to increase enzyme stability in the cases of n-hexane and isooctane and to be an absolute requirement in the case of ethyl acetate. The results obtained suggest also that, when dealing with pre-saturated phases, log P cannot be used straightforwardly to predict enzyme stability in biphasic systems.