To investigate the functional change of stromal cells along with differentiation, we used a differentiation-inducible mouse embryo fibroblast cell line, C3H10T1/2 (10T1/2). Stably determined preadipocyte and myoblast cell lines were established after a brief exposure of 10T1/2 cells to 5-azacytidine. These cell lines terminally differentiated into adipocytes and myotubes, respectively, under appropriate conditions. The hematopoiesis-supporting ability of each 10T1/2-derived cell line was examined by coculture with FACS-sorted murine hematopoietic stem cells (Thy-1lo c-kit+ Lin-). The number of granulocyte-macrophage progenitors (CFU-GM) was slightly reduced after 7 days of culture with parent 10T1/2 fibroblasts, whereas a marked increase in CFU-GM number was observed when the cells were cultured on preadipocytes. Mature adipocytes and myogenically determined cell lines, on the other hand, did not support CFU-GM growth. Further, Northern analysis showed that the preadipocyte cell line acquired the ability to produce a significant amount of stem cell factor (SCF), interleukin-6 (IL-6), leukemia inhibitory factor, and macrophage colony- stimulating factor mRNAs in response to IL-1 or lipopolysaccharide stimulation. Terminal adipocytic differentiation resulted in reduced ability to express these cytokine mRNAs. Similarly, highest IL-6 activity was detected in the supernatant of preadipocyte culture, whereas adipocytes did not secrete IL-6 even after IL-1 stimulation. Interestingly, hematopoiesis-nonsupporting myoblasts and myotubes also expressed abundant SCF mRNA, suggesting that SCF, per se, may not be sufficient for stem cell growth and survival. The 10T1/2-derived cell lines could provide a valuable tool to aid in the analysis of stromal cell development and the search for novel stromal factors.