The activities of the four enzymes catalyzing intracellular post-translational modifications of the collagen polypeptide chains were assayed in the kidneys of rats with streptozotocin diabetes. When the changes in the four enzyme activities were expressed per milligram of protein in the 15,000 X g supernatant of the kidney homogenates, there were no changes in any of the enzyme activities at four weeks and only slight increases in the prolyl and lysyl hydroxylase activities at 12 weeks after the induction of diabetes. When the changes were expressed as total enzyme activities per two kidneys, again no changes were found in any enzyme activity at four weeks, but at 12 weeks significant increases were found in all four enzyme activities, namely prolyl hydroxylase, lysyl hydroxylase, collagen galactosyltransferase, and collagen glucosyltransferase. The data would be consistent with an increased collagen synthesis in diabetic kidneys, but they do not support the hypothesis that there might be specific changes in some of these enzyme activities or in the level of certain posttranslational modifications of the collagen polypeptide chains in this disease.