In eight New Zealand white male rabbits the abdominal aorta and one iliofemoral artery was balloon deendothelialized (group A). After 2 weeks they were kept for 6 weeks on a high cholesterol diet together with eight unoperated rabbits (group B). Eight more rabbits were kept on a commercial diet only (group C). The degree of atherosclerosis was much higher in the deendothelialized Group A vessels than in the uninjured group B vessels. The activity of lactate dehydrogenase and of the rate-limiting glycolytic pyruvate kinase was significantly increased and the activity of lipoamide dehydrogenase decreased in the group A aortas. In the iliofemoral arteries a similar but statistically insignificant tendency was detected. There was no significant difference, however, in aortic lactate between the three groups. Thus, local hypoxia did not significantly contribute to the high degree of atherosclerosis in the group A animals in spite of the enzyme activity differences. Previous experience of the authors, using arterial microcathode pO2 measurements, indicates that following deendothelialization an adaptive proliferation of nutrient vessels and increased arterial oxygenation takes place. The average activity of the lysosomal N-acetyl-beta-glucosaminidase was five times and that of beta-glucuronidase, seven times higher in the Group A than Group B aortas; in the iliofemoral arteries the differences were even larger. The huge elevation of these hydrolases, which are involved in glycosaminoglycan catabolism, provides indirect indication that accumulation of glycosaminoglycans and possibly their ability to form complexes with apoB-containing lipoproteins played a major role in the much increased degree of atherosclerotic lesions in the Group A rabbits.