Articular cartilage of the proximal end of the femur from twenty-four patients with osteo-arthritis and twenty "normal" controls with fractures of neck of the femur was obtained at the time of surgical replacement of the femoral head and studied by histologic, histochemical, biochemical, and metabolic (isotopic) techniques. The data obtained demonstrated:

1. A decrease in the intensity of staining with safranin-O (a special stain for acid mucopolysaccharides) which correlated roughly with the severity of the osteo-arthritic process.

2. Essentially no change in the collagen content in the osteo-arthritic cartilage and a slight increase in the DNA and slight decrease in the hexosamine concentrations, neither of which were statistically significant.

3. A marked increase in the rates of DNA, protein and polysaccharide synthesis without significant change in the rate of RNA synthesis.

4. An inverse correlation of moderately high significance between the rates of polysaccharide synthesis and the levels of hexosamine.

On the basis of these studies, it is postulated that the chondrocyte, under conditions of chronic stress as occurs in osteo-arthritis, seems to revert to a chondroblastic state and is capable of making new cells and matrix at a much more rapid rate than is normally seen.