Light chain gene rearrangement during mammalian pre-B differentiation generally occurs in an orderly manner, beginning with kappa genes and proceeding through lambda genes. We have previously shown that human pre-B cell differentiation in vitro leads to a skewing toward lambda expression, resulting in a higher percentage of lambda+ cells than kappa+ cells. We now report that the multifunctional polypeptide transforming growth factor-beta (TGF-beta) exerts a selective inhibitory effect on the acquisition of cell surface lambda light chains during in vitro differentiation of normal human pre-B cells, giving rise to a balanced ratio (approximately 1:1) of kappa+ to lambda+ cells that resembles what normally exists in vivo. The TGF-beta effect was ablated using a neutralizing anti-TGF-beta antiserum and TGF-beta had no significant effect on the acquisition of kappa or surrogate light chains. Experiments using highly enriched pre-B cells (90-95% cytoplasmic mu+) suggested that the TGF-beta effect was directly on the pre-B cell or the pre-B cell to mu+/lambda+ immature B cell transition. The following peptides, cytokines, and antibodies had no effect on light chain acquisition or expression: substance P, vasoactive intestinal peptide, leu/met enkephalin, IL-1, IL-4, IL-7, anti-class II MHC, anti-CD24, anti-CD40, and the CD10 inhibitor phosphoramidon. A selective regulatory role for TGF-beta on normal human B cell development in the bone marrow microenvironment is suggested by these results.