The electrochemical potentiokinetic reactivation (EPR) test is commonly used to evaluate the degree of sensitization of austenitic stainless steels. It is shown in this study that the EPR test can be used to distinguish between classical sensitization, i.e., chromium depletion formation resulting from the precipitation of chromium-rich precipitates at grain boundaries and martensite-induced sensitization that takes place at lower temperatures of 450°C to 500°C. The reactivation from classical sensitization starts early, at more noble potentials than that for martensite-induced sensitization. This has been brought out in EPR results of cold-worked, warm-worked, and sensitized samples of Type 304 (UNS S30400) stainless steel.