We have assessed early changes in quiescent B cells Following cognate and bystander interaction with cloned helper T cells. Variables monitored include Ia expression, blastogenesis, G0to G1transition, and progression through cycle. We have also assessed the antigen specificity. In restriction, and dependence on membrane immunoglobulin cross‐linking of both generation and delivery of effectors that mediate B cell response. The results demonstrate that antigen presentation by quiescent B cells to T cells resulting in the generation of effectors that activate B cells is Ia‐restricted and dependent on antigen and an (mIgM and mIgD) crosslinking signal However, once generated, T cell effector functions act independently of Ia haplotype to promote Ia expression, blastogenesis, and G0to G1, transition by most small B cells. Although these responses can be mediated in T cell supernatants, further progression of B cells through S, G2, and M is only efficient when Thcells are present in cultures. Thus, results suggest that one or more Ia unrestricted, labile and/or cell‐associated factors, not active in most conventional T cell supernatants, are necessary to stimulate proliferation of small B