For the successful production of atherosclerosis, 12-week-old male rats (SHR/NCrj) were fed a high-cholesterol diet for 12 weeks with or without vitamin D₂ (VD) supplement at an initial stage, and clinical and pathological observations of them were carried out. No animals showed clinically abnormal appearence throughout the experimental period. The level of final blood pressure of the rats treated with VD was higher than that of rats untreated with VD or control rats fed normal diet. The levels of total cholesterol and β-lipoprotein of rats fed the diet with or without VD were about three times higher than those of controls. Treatment-related arterial lesions were detected only in rats with VD supplement. In the aorta, intimal fibromuscular plaques and medial sclerosis with calcification were prominent, and marked and irregular proliferation of smooth muscle cells were observed in the intima and media of the mesenteric artery with accumulation of mucopolysaccharides and lipids. Panarteritis nodosa was frequent in some of the same artery.