The effects of d-3-acetoxy-cis-2,3-dihydro-5-[2-(dimethylamino)ethyll-2-(p-methoxyphenyl)-1,5-benzothiazepine-4(5H)-one hydrochloride (diltiazem hydrochloride; CRD-401) on the hepatic, superior mesenteric and femoral arteries were investigated in dogs. The results obtained were as follows: 1. At an i.v. dose of 100 microgram/kg, CRD-401 lowered the mean aortic blood pressure (-5%). It also decreased the diastolic aortic blood pressure (-11%) but did not affect the systolic aortic blood pressure. 2. The mean aortic blood pressure decreased after injection of CRD-401, but the blood flows in the hepatic, superior mesneteric and femoral arteries increased to 33%, 31% and 17%, respectively, more than did the control values and the vascular resistances of these arteries decreased by 25%, 27% and 17%, respectively. The present study obviously demonstrates that CRD-401 has vasodilating action on the hepatic, superior mesenteric and femoral arteries.