Lipopolysaccharide (LPS)-activated B-cell blasts from C57BL/6J nu/nu spleen cells develop into IgM-secreting clones after stimulation by antigen-specific T-helper cells of C57BL/6J origin. Although induction of help is antigen-dependent, help itself acts polyclonally. 1 of 1--3 B-cell blasts is restimulated in a homologous fashion by LPS, or in a heterologous fashion by sheep erythrocyte (SRC)- or horse erythrocyte (HRC)-activated T-helper cells. The repertoire of activated B-cell blasts reflects the polyclonal nature of activation: approximately 1 in 1,000--3,000 restimulated B-cell blasts is specific for SRC, 1 in 300--1,000 is specific for HRC, and 1 in 100--300 specific for trinitrophenylated SRC (TNP30-SRC). B-cell blasts that are either H-2 compatible or H-2 incompatible with the antigen-activated T-cell help are stimulated polyclonally in similar high frequencies. Thus, neither antigen nor H-2 compatibility are required to stimulate a B-cell blast into the next cell cycle.