To study the fate of developing B cells in the presence and absence of the autoantigens to which they react, chimeric mice were constructed by injecting bone marrow cells from mice transgenic for rearranged immunoglobulin genes encoding an anti-H-2Kk antibody into irradiated recipients that did or did not express the H-2Kk antigen. In the presence of H-2Kk, the anti-H-2Kk-specific B cells were deleted from the spleen and lymph nodes, whereas in its absence, anti-H-2Kk cells were abundant. B cells bearing a low level of membrane immunoglobulin with the anti-H-2Kk idiotype were found in the bone marrows of H-2Kk recipients, suggesting that clonal deletion of autoreactive cells was occurring in the pre-B-cell to B-cell transitional stage of B-cell development.