A genetically selected line of White Carneau pigeons (WC-2) was studied in an attempt to relate changes in composition and content of aortic glycosaminoglycan (GAG) to increased atherosclerosis susceptibility. The WC-2 pigeons were fed an atherogenic diet for 3 months and, when compared to randomly bred White Carneau (RBWC) controls, they showed similar plasma cholesterol concentrations but significantly greater aortic atherosclerosis. In the WC-2 pigeons, 35% of the aortic surface was covered with plaque compared with only 12% in RBWC pigeons; WC-2 birds showed cholesterol contents of 3.3 mg/aorta/500 g body weight, while the RBWC birds had only 0.9 mg/aorta/500 g body weight. After papain treatment of delipidated dried artery, the aortic GAG were isolated, purified using cetylpyridinium chloride, and identified and quantitated by a combination of procedure including selective enzymatic digestion and electrophoresis. In both pigeon groups, aortic GAG included 8% hyaluronic acid, 11% dermatan sulfate, 15% heparan sulfate, and 66% chondroitin sulfate. For the entire group, total aortic GAG content was 35% greater in WC-2 pigeons. Since we did not know if this increase in GAG was simply due to increased atherosclerosis in the WC-2 birds, we sorted the pigeons into matched groups representing minimal, moderate, and severe atherosclerosis on the basis of aortic cholesterol content. At all levels of cholesterol, all GAG contents were greater in the aortas of WC-2 pigeons. The accumulation of dermatan sulfate was 30% higher than in RBWC birds in the minimal arteriosclerosis group, 101% higher in the moderate group, and 53% higher in the severe group. Hyaluronic acid tended to decrease as aortic cholesterol contents increased in WC-2 pigeons. Reduced hyaluronic acid and increase dermatan sulfate may suggest the presence of an altered hyaluronic acid-dermatan sulfate-containing proteoglycan aggregate in the intercellular matrix of the WC-2 pigeon aorta. Possible consequences include increased artery permeability and a binding and retention of lipoproteins in the artery wall. These factors may explain why atherosclerosis develops at an increased rate in the WC-2 pigeon.