The results of coronary arteriography were compared in 102 patients (55 non-diabetics and 47 diabetics) with angina. The lesions noted an arteriography were more severe in the diabetic patients: more frequent stenosis in the common trunk and three branches, and present in greater numbers (more than 4 in more than a half of the patients), with only a moderate proximal bed in 65% of the cases. By-pass operations can only be performed, therefore, in 32% of these patients as against 54% for the non-diabetic anginal patients. The operative risk also appears to be increased (1 death and 6 complications in 10 by-pass operations). It was also demonstrated that with similar lesions of the common trunk, the diabetics have radiological signs of a greater incidence of cardiomegaly and generalized hypokinesia of the left ventricle than non-diabetics. By-pass operations are impossible in about 85% of patients because of ischemic signs or evidence of necrosis in the ECG recordings of diabetic patients with angina.