Open joint wounds were made in immature and mature rabbit knees by surgical arthrotomy. The wounds of the right knees were packed open for 5 days and the left knee wounds were closed primarily. The biochemical studies were selected to determine the effect of our treatment regimen on changes in the metabolism of articular cartilage and synovium. Neither closed nor open treatment produced significant changes in enzyme activities measured in the articular cartilage as compared to the controls in either immature or mature rabbits. Most of the synovial enzymes were elevated in the injured joints. There were, however, no significant differences in enzyme activity between the joints treated by either open or closed methods. Our findings suggest that short-term open treatment wounds does not cause matrix degradation in the cartilage nor affect the synovium more than simple arthrotomy.