Abstract Conditioned media (CM) from various marrow subpopulations (MBA series) were examined for their effects on growth and maturation of marrow-derived osteoblastic cells, MBA-15. CM harvested from a stromal adipocytes, 14F1.1, stimulated cell growth, collagen but not non-collagenous proteins synthesized by MBA-15 cells. Alkaline phosphatase activity was inhibited under the same culture conditions. These results were associated with morphological changes, i.e.,the large cuboidal MBA-15 cells acquired a fibroblast-like appearance. Exposure of MBA-15 cells to known growth factors: BMP-2, TGFβ, IGF-I and PDGF or combined with 14F1.1 CM resulted in a dominant effect of the latter. This may imply that marrow adipocytes produce factor/s that participate in the stromal regulation of osteoblastic functions.