This proposal is aimed at isolating and purifying a molecule obtained from human heterotopic bone. This molecule stimulates many of the cell parameters associated with bone formation. In the Specific Aims of this grant we propose to examine the phenotypic changes which occur in bone and cartilage cells after exposure to the molecule and to characterize the interactions of other one target hormones with the factor. We will also determine if the stimulatory molecule obtained from a pathological tissue if the same as the molecule obtained from normal tissue.