Soluble sodium chondroitin sulphate, from bovine ribs or puppy epiphyseal plate, at a concentration 80mm in terms of glucuronate, decreased the amounts of calcium and phosphate precipitated from a solution 6.9mm in phosphate and 6.9 or 13.8mm in calcium, buffered in the pH range 6.6-8.2 with 20-25mm-collidine and 5-20mn-hydrochloric acid when incubated for 2hr. at 30 degrees , and for 0.25-24hr. when buffered at pH7.0. 2. An insoluble fraction of puppy epiphyseal plate, containing chondroitin sulphate and collagen, was found to have the same effect at lower concentrations of chondroitin sulphate and a higher calcium/chondroitin sulphate glucuronate ratio, but the formation of calcium phosphate from calcium bound to this material appeared to proceed more rapidly than from calcium in solution, when both were present in the same system. 3. The implications of these results are discussed in relation to the calcium/chondroitin sulphate glucuronate ratios found in different parts of non-calcifying and calcifying cartilage in vivo and to the calcium and phosphate gradients between blood and calcified tissue.
