The purpose of this study was to test for the presence of matrix metalloproteinase (MMP) in synovial fluid of sheep with experimentally induced temporomandibular joint (TMJ) osteoarthrosis (OA) at various time intervals. Twenty-one sheep were used in this study. TMJ OA was induced bilaterally in 18 sheep and 3 sheep were used as controls. Each experimental group had 3 sheep, and the groups were killed at 2, 4, 6, 8, 12, and 24 weeks postoperatively. Synovial fluid was collected at killing, and the joints were evaluated histologically. Gelatin zymography was performed to detect the presence of MMPs in the synovial fluid. TMJ OA gradually progressed over time. ProMMP-2 was detected in all experimental groups. However, the activated form of MMP-2 was only detected at 2 and 4 weeks postoperatively. Activated MMP-2 activity correlates with initial articular cartilage destruction rather than with the progression of OA in the sheep TMJ. Copyright 2002 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 60:66-72, 2002