Rabbit knee joints were immobilized in the extended position for 1 to 6 days, and examined by means of histochemical techniques. In the articular cartilage matrix, the earliest change was the loss of affinity for metachromatic stains, confirming earlier observations. The affinity of cartilage for high iron diamine and alcian blue stains was also diminished, although less dramatically; these stains demonstrated the concentration of glycosaminoglycans more accurately than metachromatic stains. With the colloidal iron method, changes were seen in the chondrocytes before there was any loss of affinity for metachromatic stains. Following only 1 or 2 days of immobilization, the chondrocytes in the gliding surface of the joint stained intensely with colloidal iron whereas those in the controls stained very minimally.