The venodilating action of nipradilol was investigated by monitoring arterial blood pressure (BP), cardiac output (CO), heart rate (HR) and central venous pressure (CVP) in pithed rats treated with dihydroergotamine (DHE). DHE increased CVP and produced a simultaneous rise in BP and CO without appreciable changes in total peripheral resistance (TPR) and HR, indicating that DHE reduces venous capacity through venoconstriction. Nipradilol caused a fall in CVP, BP and CO without changing the TPR in the DHE-pretreated rat. By comparison, hydralazine reduced BP and TPR without changes in CO. Propranolol produced only a transient decrease in BP and TPR. These results indicate that nipradilol dilates venous capacitance vessels and thereby decreases cardiac filling pressure in animals with high venous tone, whereas hydralazine preferentially dilates resistance vessels.