Subtotal synovectomies were carried out on the knee joints of rabbits. The synovial membrane regenerated in a matter of sixty days. During the time when synovial membrane and synovial fluid were virtually absent from the joint the cells of the articular cartilage exhibited no impairment in their ability to absorb S35 and deposit it in the matrix. The cartilage, however, when stained metachromatically with toluidine blue lost metachromasia to a varying degree during the time of synovial regeneration. It is felt that this is due to enzymatic degradation of the protein-polysaccharide of the ground substance and that this degradation continues until synovial regeneration is complete.