There are no reports on rates of amino acid racemization in bones. To investigate the possibility of estimating age by evaluating amino acid residue racemization in human bones, a heating experiment was performed and the rate of aspartic acid racemization was determined using the Arrhenius equation. Assuming an annual mean temperature of 15 degrees C, the rate constant (k) for aspartic acid racemization in bone was calculated, and the racemization rate at 15 degrees C k (y) was 4.1036 x 10(-9)--much lower than that of dentin. These results suggest that it is more difficult to accurately determine age by analyzing aspartic acid residues in bone than in dentin.