Prolylhydroxylase and galactosylhydroxylsyl glucosyl (GGH) transferase were assayed in cells cultured from cartilage and synovium (adipose type) removed from normal and adjuvant arthritic rat knees. There was a significant increase in prolylhydroxylase in chondrocytes from arthritic knees compared to the normals but no change in GGH transferase activity was found. In the cells derived from the synovium no variation in either enzyme was observed. No significant changes in DNA or protein content was found in either type of cells from the arthritic joints. Comparison of the prolylhydroxylase activity in the supernatant and pellet fractions prepared from chondrocytes from normal and arthritic joints, demonstrated that the majority of the activity was recovered in the supernatant fraction rather than the pellet in arthritic chondrocytes. The data presented indicate that the degree of hydroxylation of cartilage collagen alters in arthritis.