Objectives. The effects of hypertension and diabetes on the physical properties of large arteries were compared in men.Background. Although these two diseases are linked to vascular stiffening, no study has analyzed whether the arterial rigidity in diabetes is as substantial as in hypertension.Methods. Noninvasive measurements of brachial artery mean pressure, diameter (pulsed Doppler study) and compliance (pulse wave velocity) were obtained in 29 men: 11 control subjects, 9 hypertensive nondiabetic patients and 9 diabetic normotensive patients. Individual diameter- and compliance-pressure curves extrapolated from the measured diameter and mean pressure point with a logarithmic elastic model permitted calculation of isobaric diameter and compliance at the same pressure in each subject.Results. Compared with control subjects, hypertensive patients had a larger brachial artery measured diameter and isobaric diameter (p < 0.01) and lower measured and isobaric compliance (p < 0.001, p < 0.01). Compared with control subjects, diabetic patients had lower measured and isobaric compliance (p < 0.01). Comparison of diabetic and hypertensive patients showed that measured diameter and isobaric diameter were decreased in the former (p < 0.01). In the control and hypertensive groups, mean pressure correlated positively with measured diameter and isobaric diameter (p < 0.01) and negatively with measured and isobaric compliance (p < 0.001 and p < 0.01, respectively). In the control and diabetic groups, fasting glucose correlated negatively with measured and isobaric compliance (p < 0.01, p < 0.05).Conclusions, Intrinsic alterations of the large artery independent of a stretching pressure effect reduce arterial elasticity similarly in those with hypertension or diabetes. The loss of compliance is related to the chronic elevation of blood pressure in hypertension and to that of glycemia in diabetes and is associated with a relative large artery vasoconstriction in diabetic patients as compared with patients with hypertension.