Recent advances in long‐term bone marrow (BM) culture techniques have allowed investigators to dissect cellular components responsible for lympho‐hematopoiesis. Consequently, a number of “stromal” cell clones have been developed which are capable of supporting B lineage lymphocyte growth and proliferation in vitro by direct cell‐cell interactions and the release of cytokines. While much work has focused on the support function of these cells, questions remain regarding their own differentiation potential. We have examined adipo‐genesis in the cloned BM stromal cell, BMS2. The presence of hydrocortisone, methylisobutylxanthine, or 30% fetal calf serum each accelerated adipocyte differentiation. This process was accompanied by the accumulation of triglycerides and cholesterol esters along with the induction of adipocyte‐specific enzymes. Likewise, the steady‐state level of mRNA transcripts increased for genes related to lipid metabolism. However, the pattern of mRNA expression in BMS2 adipocytes differed from that of a well‐established, pre‐adipocyte cell line, 3T3‐L1, with respect to the following genes: glycerol phosphate dehydrogenase, CAAT/enhancer binding protein and angiotensinogen. Adipocyte BMS2 cells retailed the ability to support stromal cell‐dependent B lineage lymphocytes in methylcellulose assays. The adipocytes continued to express macrophagecolony‐stimulating factor mRNA constitutively and interleukin 6 mRNA in an inducible manner, similar to the BMS2 pre‐adipocytes. Together, these data document a close developmental relationship between a specialized fibroblasts and adipocytes in the BM and suggest that adipocyte stromal cells may play an active role in lympho‐hematopoiesis.