Anterior cruciate ligament transection (ACLT) in the dog produces changes in the articular cartilage of the unstable knee that are consistent with those of osteoarthritis (OA). To determine whether the degrees of severity of OA cartilage changes, of synovitis, and of synovial iron deposition were related to adequacy of hemostasis at the time of ACLT, a modified surgical technique was devised, whereby electrocautery was used to obtain meticulous control of bleeding when the ligament was severed and irrigation was used to remove intraarticular blood before closure of the joint. When no particular attention was given to hemostasis, 69% of the dogs showed synovitis in the OA knee 10 weeks after ACLT; when electrocautery and irrigation were used to maintain hemostasis, synovitis was present in only 24% of the OA knees 10 weeks after ACLT (P less than 0.01). Iron deposits were present in 75% of synovial samples obtained after routine ACLT, but in only 6% (P less than 0.001) when attention was given to hemostasis. Hypertrophy of articular cartilage, chondrocyte cloning, fibrillation, and changes in tangential zone chondrocytes were less prominent in the OA knee when electrocautery and irrigation were used. However, the water content, uronic acid concentration, and rate of net 35S-labeled glycosaminoglycan synthesis were similarly increased regardless of the surgical technique used, and presumably, these changes reflect the reaction of joint cartilage to mechanical instability in this model of OA.