An analytical protocol for the analysis of proteoglycans and proteins extracted from small sections of cartilage has been applied to the upper and lower parts of the epiphyseal growth plate of normal rats and rats with strontium-induced rickets. Only one polydisperse proteoglycan population was found in each of the four tissue portions. In strontium-induced rachitic animals the aggregability of proteoglycan monomers with hyaluronate was considerably increased in the lower part of the growth plate. The proteoglycans in the upper portion of the epiphysis contained somewhat less of chondroitin sulfate and keratan sulfate both in normal and strontium-induced rachitic rats. The chondroitin sulfate chains were somewhat larger in samples from strontium-induced rachitic rats compared with controls while in all groups about 90 per cent of the galactosamine in chondroitin sulfate was sulfated at position four. The findings of an altered composition of proteoglycans in strontium-induced rickets demonstrate that strontium not only prevents the mineral growth but may also induce the chondrocytes to produce a matrix with a different macromolecular composition.