ABSTRACT Male albino rabbits were injected with prednisone 2 mg/kg body weight, daily for two weeks. The aortic content of acid mucopolysaccharides and the synthesis of sulphated acid mucopolysaccharides decreased, whereas the collagen content remained unchanged as compared to the saline injected controls. Prednisone induced no gross or microscopic changes in the aortae. The alterations were related to those previously reported in human skin and vein biopsies and may be of pathogenic significance in the vascular fragility following long-term treatment with glucocorticoids.