This study investigates the formation of bone-like tissue in vitro using stromal cells derived from the bone marrow of young adult rats. The cells were cultured in α-minimal essential medium supplemented with fetal bovine serum, antibiotics, and ascorbic acid, and then subcultured for 20-30 days. Cultures were treated with either Na-β-glycerophosphate, dexamethasone, or both. Only cultures treated with both β-glycerophosphate and dexamethasone formed collagenous, mineralized nodules with characteristics similar to bone. These nodules exhibited alkaline phosphatase activity, composed predominantly of type-I collagen, and contained osteonectin and Gla-protein. X-ray microanalysis confirmed the presence of Ca and P, and X-ray diffraction indicated the mineral to be hydroxyapatite. Additionally, the nodules showed bone morphogenetic protein-like activity, as evidenced by the induction of cartilage in relation to muscle when implanted in rats. The findings demonstrate that bone-like tissue can be synthesized in vitro by young-adult bone marrow stromal cells, provided the medium contains both β-glycerophosphate and dexamethasone.This study investigates the formation of bone-like tissue in vitro using stromal cells derived from the bone marrow of young adult rats. The cells were cultured in α-minimal essential medium supplemented with fetal bovine serum, antibiotics, and ascorbic acid, and then subcultured for 20-30 days. Cultures were treated with either Na-β-glycerophosphate, dexamethasone, or both. Only cultures treated with both β-glycerophosphate and dexamethasone formed collagenous, mineralized nodules with characteristics similar to bone. These nodules exhibited alkaline phosphatase activity, composed predominantly of type-I collagen, and contained osteonectin and Gla-protein. X-ray microanalysis confirmed the presence of Ca and P, and X-ray diffraction indicated the mineral to be hydroxyapatite. Additionally, the nodules showed bone morphogenetic protein-like activity, as evidenced by the induction of cartilage in relation to muscle when implanted in rats. The findings demonstrate that bone-like tissue can be synthesized in vitro by young-adult bone marrow stromal cells, provided the medium contains both β-glycerophosphate and dexamethasone.