Osteopontin is a major non-collagenous bone matrix protein secreted into the mineralizing extracellular matrix by osteoblasts during bone development. Recombinant human osteopontin (hOPN) that includes the Arg-Gly-Asp (RGD) cell recognition site was expressed in Escherichia coli and the purified osteopontin increased cell adhesion, proliferation and differentiation of osteoblast cells (p < 0.05).