Antibody V gene expression was studied in a subpopulation of murine B cells (Ly1 B) which was enriched by cell transfer and had earlier been shown to persist in the immune system over long periods of time. Among 17 hybridomas derived from Ly1 B cells of two different mice, eight were progeny of only three different B cell precursors which apparently had expanded to clones of large size, in the absence of detectable somatic mutation of their antibody V regions. Furthermore, several clonally independent cells expressed identical, unmutated V genes. These data define a novel pathway of B cell development in which cells expressing a selected set of germline antibodies are continuously propagated in the organism. A Ly1 B cell leukemia derived from a similar transfer experiment expressed a VH gene that had been isolated in three independent Ly1 B cell hybridomas, suggesting that the leukemic cells had been equally selected in this pathway.