The metabolism of proteoglycans in normal growth plate and the changes in growth plate morphology induced by diabetes and malnutrition were studied in rats. The proteoglycans had a significantly faster turnover (half-life measured with [35S]sulfate labeling: 25-30 h) than the cells in the growth plate. Morphometric studies showed significant reductions of cell number, zone height, and [3H] thymidine incorporation in growth plates from rats with untreated streptozotocin-induced diabetes compared to normal rats. Similar, although less pronounced alterations were observed in malnourished, nondiabetic rats. Disaggregation and degradation of proteoglycans are probably necessary prerequisites for calcification. Our data indicate that the proteoglycans are in a dynamic state of rapid biosynthesis and degradation throughout the growth plate with a shift in the balance at the calcification front toward less synthesis and more degradation.