Angiotensin receptor blockers (ARB) have been emerging as drugs to treat atherosclerosis. The effectiveness of the ARB losartan at reducing atherosclerosis was compared with that of ACE inhibitors in hypertensive patients. A total of 50 patients with hypertension were divided into 3 groups: a control group receiving neither an ARB nor an ACE inhibitor (n = 14), a losartan group (n = 22) receiving 50 mg/day of losartan, and an ACE inhibitor group (n = 14) receiving either 5 mg/day of enalapril or 5 mg/day of imidapril. Atherosclerosis was evaluated based on the intima-media thickness (IMT) of the common carotid artery measured by B-mode ultrasound at baseline and after approximately 12 months of treatment. After the treatment, IMT significantly decreased with losartan (from 0.87 +/- 0.14 to 0.79 +/- 0.16 mm, P < 0.05) and with ACE inhibitor (from 0.81 +/- 0.14 to 0.74 +/- 0.11 mm, P < 0.05). The reduction was comparable between the two groups, -0.078 +/- 0.136 with losartan and -0.073 +/- 0.109 mm with ACE inhibitor, and the rate of the reduction was similar between the two drugs; -0.098 +/- 0.142 mm/year with losartan and (-0.076 +/- 0.118 mm/year) with ACE inhibitor. On the contrary, IMT did not change in the control group (from 0.90 +/- 0.20 to 0.95 +/- 0.26 mm) during the treatment period. Concomitant medication and coronary risk factors such as hyperlipidemia, diabetes mellitus, and smoking did not differ significantly among the groups. The antiatherosclerotic effect of losartan on the carotid artery was comparable to that of ACE-inhibitors, and less adverse effects, such as coughing that occurs with ACE inhibitors, were observed. Losartan appears to be a better alternative to ACE inhibitors for treating atherosclerosis in Japanese hypertensive patients.