On the age estimation by the amino acid racemization analysis of dentin, besides the utilization of aspartic acid (Asp) as described in earlier reports, we further studied relationships between the D/L ratios based on glutamic acid (Glu) as well as alanine (Ala) and actual ages. The study was followed up by comparing racemization velocities of the three amino acids under some heating experiments. At four steps (6, 24, 48 and 72 hours) of hydrolysis, the coefficient values of D/L ratio of each amino acid and actual age were calculated as 0.986 to 0.994 for Asp, 0.522 to 0.806 for Glu, and 0.577 to 0.737 for Ala. The data indicate that Asp gives an extremely good result. Glu and Ala do provide reliable D/L ratios, however they are not in proportion to actual ages. Consequently, Glu and Ala seem to be much less suitable for utilization in age estimation. Reaction rate constants (k.yr-1) of racemization of Asp, Glu and Ala in antemortem teeth were 5.3825 x 10(-4), 5.1000 x 10(-5) and 2.3875 x 10(-5), respectively. Those in teeth left drying at 15 degrees C were 2.4850 x 10(-8), 1.9119 x 10(-9), and 1.11450 x 10(-9), respectively. Assuming that the reaction velocity of Asp be 1 in both living and dry states, that of Glu were calculated as 0.09 and 0.08, that of Ala, 0.04 and 0.05, indicating very similar rates. The result confirmed that both Glu and Ala gave considerably slow racemization velocities as compared with Asp.