Objective: To test the hypothesis that osteogenic protein-1 (OP-1) can stimulate differentiation of adipose-derived stem cells (ASDCs) into an osteoblastic lineage and produce mineralizing tissue in vitro. Methods: ASDCs were isolated from inguinal fat pads of mice, expanded 2 passages and plated in 8-well chambered slides at 2 x 104 cells/well. Cells were subjected to one of four protocols (n=3): G1 – control medium, G2 – control + 0.1 uM dexamethasone, G3 – control + dexamethasone + 250 ng/mL OP-1, G4 – control + OP-1. Bone production was assessed by no. and size of mineralized nodules (21 d), and extracellular osteopontin (OPN) production via ELISA (8 & 21 d). Results: For calcified nodule deposition at 21d, G4 =G3 > G2=G1 (p≤ 0.05). OPN (ng/mL) at 8 d: G3 (66±4) = G4 (65±8) > G2 (38±3) > G1 (14±2). OPN at 21d: G4 (59±10) = G3 (53±5) = G2 (49±14) > G1 (22±2) (all p≤0.05). Conclusion: The results supported the hypothesis that OP-1 induces osteogenic differentiation of ASDCs. Certain osteogenic mediators may limit the ability of OP-1 to promote osteogenesis.