Biochemical studies done on the connective tissues of hip joints from beagles at different ages showed that the DNA and hexosamine content were reduced by about 50 per cent from birth to one year of age in articular cartilage, while the hydroxyproline content increased with age. The connective tissues of hip joints contained measurable quantities of soluble collagen at birth, but as animals became older, soluble collagen content diminished, and after six months of age essentially only insoluble collagen was found. The rates of protein and polysaccharide formation were significantly higher in the samples from newborn puppies than in those from one-year-old dogs; the rate of collagen synthesis in cartilage decreased dramatically. The data indicated that metabolic activity per individual cell was reduced in the cartilage samples from mature dogs. The hydrolytic enzyme activities decreased in the tissues with age, primarily because of a decreased number of cells per unit weight of cartilage.