ST2 cells, a cloned stromal-cell line from mouse bone marrow have the phenotypes of osteoblasts and hematopoietic supporting cells, but little is known about the adipogenesis in this cell line. We found that treatment of ST2 cells with a cocktail, a combination of insulin, dexamethasone (DEX) and 3-isobutyl-1-methylxanthine (IBMX), induced adipocyte differentiation. The cells were adipocytic, as seen by the accumulation of triglycerides and with lipid droplets stained with Oil Red O. Expressions of the adipogenic transcriptional factors peroxisome-proliferator-activated receptor gamma and CCAAT-enhancer binding protein alpha were stimulated, triggering the expression of the late adipocyte-specific marker alpha-glycerophosphate-3-dehydrogenase. Unlike another bone marrow stromal cell line PA6, ST2 cells responded to the adipogenic effects of insulin, as do the extramedullary preadipocytes 3T3-L1. Like PA6 and 3T3-L1 cells, adipogenesis in ST2 cells was inhibited by 1,25-dihydroxyvitamin D3, retinoic acid, tumour necrosis factor alpha, and transforming growth factor beta. Therefore, ST2 cells can differentiate into osteoblasts, adipocytes, and hematopoietic supporting cells, in which the process of adipogenesis differs from that of bone marrow preadipocytes PA6, and resembles that of the extramedullary preadipocytes 3T3-L1.