Orthopedic procedures expose articular cartilage to operating room air for varying periods of time as long as two hours. Articular cartilage is dense white, glossy and smooth, and is composed of chondrocytes, collagen, and a hyaline matrix made up of proteoglycan molecules. Articular cartilage is a specialized tissue containing 75 to 85% water. Most of the water is trapped in a gel of matrix collagen and proteoglycan and is freely exchangeable with the synovial fluid and blood. Only about 6% of cartilage water is tightly bound. Theoretically, since cartilage gel is hyperhydrated, the water content is important in maintaining cartilage resiliency and lubrication of the articular surfaee. If a pathologic state is associated with reduction on water content, these properties may be altered, leading to impaired joint function. We reproduced the O.R. situation by exposing one knee of 24 mature New-Zealand white rabbits to smbient air (20–22℃) for 30 minutes to 2 hours, the opposite knee serving as a control. Following exposure, the joints were closed snd the animal resumed cage activity for 1 day prior to sacrifice, at that time cartilage was removed from both exposed and control joints and prepared for gross, light microscopy and electron microscopy. We observed cartilages which were sacrificed at 1 week after operation, 2 weeks after and 4 weeks after for varying periods of exposing time in same method. The results were as follow ; 1. A distinct color change was seen in the exposed cartilage in groups which were sacrificed postoperative at 1 day ; However minimal change was detected in each group sacrificed at 1 week & 2 weeks later, and no change was seen in each group sacrificed postoperative at 4 weeks. 2. Exposure to room air for 30 minutes produced chondrocyte necrosis in the superficial zone of rabbit articular cartilage. Exposure for 1 hour or longer produced chondrocyte necrosis up to radial zone. 3. Chondrocyte necrosis was not seen in each group for varying periods:0f air exposure microscopically, which sacrificed postoperative at 1 week. 4. Proteoglycan content was minimal at 1 week postoperatively in each group ; However proteoglycan content increased progressively with time. 5. Change in cellularity were consistent with cartilage damage. Seemingly, exposing articular cartilage to air for 2 hours caused reversible cartilage damage.