This work investigated the kinetics of catabolism and the catabolic fate of the newly synthesized 35 S-labelled proteo-glycans present in explant cultures of tendon. Tissue from the proximal region of bovine deep flexor tendon was incu-bated with [ 35 S]sulfate for 6 h and then placed in explant cultures for periods of up to 15 days. The amount of radi-olabel associatedwithproteoglycans and free [ 35 S]sulfate lost to themediumand retained in thematrixwas determined for each day in culture.