The nonspecific stimulant of the immune response salmozan (Sal) increases the number of PFC against SRBC in intact mice, B mice (thymectomized, irradiated and reconstituted with embryonic liver cells), and in mice pretreated with cyclophosphamide (CY). This effect was decreased in mice pretreated with SRBC and CY. The subsequent injections of SRBC and Sal into tolerant mice did not increase the response under study. It is concluded that the effect observed is due to partial alteration of antigen-specific B cells of tolerant mice and this alteration cannot be explained by the lack of the regeneration of membrane immunoglobulins.