The composition of buried bone changes with time. Hydroxyapatite, the major inorganic component, undergoes very slow exchange with ionic species from groundwaters. The nitrogen content decreases as the collagenous material is removed and replaced, in part, by inorganic salts. The rate of nitrogen loss is generally much greater than the rate of the exchange reaction. The results of carbon, hydrogen, nitrogen, and ash analyses for samples of ivory excavated in the Ancient Near East reveal a similar compositional variation. In excavated specimens of known provenance (Hasanlu, Northwest Iran; Nimrud, Iraq; and Acem Hüyük, Anatolia) the nitrogen content was lte 0.5% (except for black ivories from Hasanlu) whereas the nitrogen content of modern elephant ivory is >5.0%. The percent ash, as combustion residue, was >80% for excavated ivory com pared with ca. 55% for modern elephant ivory. The generality of these results for many samples has suggested the use of these data to develop criteria for the chemical examination of artifacts of doubtful provenance.