Cell proliferation of normal and osteoarthitis (OA) osteoblasts in response to insulin-like growth factor (IGF)-1 stimulation. Cells were plated at 10,000 cells/cm2 in 96-well plates and incubated overnight in Ham F12/DMEM media containing 10% FBS. Cells were then serum-starved for 24 hours in the same media containing 0.5% BSA then treated with or without 50 ng/ml IGF-1 in the presence or not of 10 μM PD98059 (PD) for 24 hours followed by incubation with bromodeoxyuridine (BrdU) for their last 24 hours of incubation in the same media. BrdU incorporation was then evaluated following the manufacturer's instructions. Results are expressed as mean OD units ± SEM for three normal and four OA osteoblast preparations.