Knowledge of rates of protein turnover is important for a quantitative understanding of tissue synthesis and catabolism. In this work, we have used the racemization of aspartic acid as a marker for the turnover of collagen obtained from healthy and pathological human intervertebral disc matrices. We measured the ratio of the d- and l-isomers in collagen extracted from these tissues as a function of age between 16 and 77 years. For collagen taken from healthy discs, the fractional increase of d-Asp was found to be 6.74 × 10^–4/year; for degenerate discs, the corresponding rate was 5.18 × 10^–4/year. Using the racemization rate found previously for the stable population of collagen molecules in dentin, we found that the rate of collagen turnover (k_T) in discs is not constant but rather a decreasing function of age. The average turnover rate in normal disc between the ages of 20 and 40 is 0.00728 ± 0.00275/year, and that between the ages of 50 and 80 is 0.00323 ± 0.000947/year, which correspond to average half-lives of 95 and 215 years, respectively. Turnover of collagen from degenerate discs may be more rapid than that found for normal discs; however, statistical analysis leaves this point uncertain. The finding of a similar correlation between the accumulation of d-Asp and that of pentosidine for three normal collagenous tissues further supports the idea that the accumulation of pentosidine in a particular tissue can, along with the racemization of aspartic acid, be used as a reliable measure of protein turnover.