Collagen synthesis by osteoarthritic cartilage from dogs that had undergone anterior cruciate ligament transection was measured in short-term organ cultures and chondrocyte suspension cultures. Slices of osteoarthritic cartilage from unstable knees 2, 6 or 12 weeks after anterior cruciate ligament transection converted approximately 10% of the total incorporated 14C-proline to 14C-hydroxyproline, while the value for cartilage from the contralateral knee or from knees of normal control dogs was generally less than 1%. The increase in collagen synthesis in the osteoarthritic cartilage was not related to the duration of knee instability, but was greater in grossly fibrillated cartilage than in the total pooled cartilage from the osteoarthritic joint. The collagen that was synthesized was predominantly type II, although some type XI and/or type V collagen was also synthesized. Chondrocytes isolated from osteoarthritic knee cartilage of dogs 12 weeks after anterior cruciate ligament transection showed changes in collagen synthesis similar to those seen in the cartilage organ cultures. As in the organ culture studies, type II collagen was the predominant species synthesized. When cell-associated collagen was considered, type II collagen accounted for 87+/-7% of the total collagen synthesized and retained by the osteoarthritic chondrocytes. The corresponding value for cells from the contralateral knee was 63+/-10%. Since the collagen fiber in articular cartilage is a heteropolymer of type II, type XI and type IX collagen, it is likely that the newly synthesized collagens in this model of osteoarthritis form fibers that are phenotypically different from those in normal articular cartilage.