Recent stduies have identified major disconcordances between 14 C and amino acid racemization (AAR)-deduced age estimates in some bone samples. Prior to our examination of several factors that have been suggested as contributing to producing anomalous AAR-deduced ages, we have quantified the reproducibility and accuracy of our work-up procedures and instrument operation for D/L aspartic acid analysis by using high performance liquid chromatorgraphy on both standard mixtures and bone samples of varying organic content. Our average instrumental and analytical variability rarely exceeds 2per thousand to 3per thousand. Using these procedures, we have examined variations in D/L aspartic acid ratios in single bone samples and in bones from different skeletons deposited at the same time in the same burial environment. In modern bone (high amino acid nitrogen content), D/L aspartic acid values in the total hydrolysate and HCL-insoluble fraction were found to be similar while the HCL-soluble fraction exhibits about a 30per thousand higher D/L aspartic acid ratio. In our fossil bone sample (low amino acid nitrogen content), D/L aspartic acid ratios were again highest in the HCl-souble fraction, but there was also a significant difference between the total and insoluble fraction. We have also observed major variations in D/L aspartic acid ratios in the total hydrolysates of bone samples from a series of human skeletons buried at the same time and thus subjected to a similar temperature history. In our samples, diagenetic effects as indicated by low nitrogen values and attenuation of the collagen-like Gly/Glu ratio are associated with the observed variabliltiy in the D/L aspartic acid values.