The existence of autoreactive B cells was predicted by theoretical considerations and, recently, confirmed by direct experiments. The aim of the present work was to investigate if the capacity of self-reactive B cells to be activated with different polyclonal B-cell activators (PBA) reflects the heterogeneity of the response as seen in all the Ig-positive cells. We injected mice with dextran sulfate, lipopolysaccharide from Escherichia coli 055:B5, and purified protein derivate of turbercle bacteria RT32 and studied the complement-dependent cytotoxicity against syngeneic spleen cells caused by the sera from injected mice with regard to the different parameters used for characterization of B-cell subpopulations. It was found that the capacity of self-reactive B cells to secrete antibodies reflects the polyclonal-activating capacity of the PBA used. The implications of these findings for the understanding of the triggering mechanism of B lymphocytes and for self-nonself discrimination are discussed.