Abstract The low sulfated chondroitin sulfate fraction isolated and purified from bovine cornea was shown to consist of numerous molecular species ranging in their sulfate-hexosamine ratio from 0·2 – 0·9. On incubation of cornea in vitro, under appropriate conditions in the presence of 35S-sulfate, all chondroitin sulfates were obtained in the 35S-sulfate labelled form, but in a 5-min pulse experiment the specific radioactivity of the low sulfated chondroitin sulfates was up to 50% higher than that of the higher sulfated chondroitin sulfates. On further incubation in 35S-sulfate-free medium, the bulk of the radioactivity shifted from the lower to the higher sulfated chondroitin sulfates, the specific radioactivity of the latter being three times higher than that of the low sulfated chondroitin sulfates. The results presented are consistent with the assumption that a sulfate-free or low sulfated chondroitin is the biological precursor of the chondroitin sulfate population in bovine cornea.