Protein synthesis by human chondrosarcoma tissue and normal articular cartilage was studied in organ and primary monolayer cell culture systems. Protein synthesis by cell cultures was evaluated at 2,7, and 21 days after plating. When compared to normal, incorporation of ³H-proline and ³⁵S-methionine into proteins was elevated in chondrosarcoma samples under both culture conditions. Hydroxyproline analyses of tissue hydrolysates indicated that chondrosarcoma samples contained significantly less collagen than normal articular cartilage, yet were incorporating significantly greater amounts of ³H-proline into ³H-hydroxyproline. Collagen production by cell cultures was assessed by digestion of samples with purified clostridial collagenase. Chondrosarcoma cells produced more collagenase-sensitive protein than normal cells at all intervals. SDS polyacrylamide gel analyses of all preparations showed two collagenase-sensitive proteins with apparent molecular weights of 165,000 and 175,000. Decreased synthesis of another major protein, apparent molecular weight 210–220,000 was noted in chondrosarcoma preparations in both culture systems.