Abstract: The present invention includes a crystal structure of the kinase domain of c-fms and a methodology to produce diffraction quality crystals of the c-fms kinase domain by heterologous substitution of the kinase insert domain. Also included in the invention is the structure of the c-fms kinase domain in liganded form for use in the discovery of inhibitors of c-fms for the treatment of diseases caused by inappropriate activity of c-fms. The present invention includes descriptions of the X-ray diffraction patterns of the crystals. The diffraction patterns allow the three dimensional structure of c-fms to be determined at atomic resolution so that ligand binding sites on can be identified and the interactions of ligands with amino acid residues can be modeled.