The hemodynamic effects of sulfinpyrazone were investigated in 12 anesthetized dogs. Bolus injections into a coronary artery (1--500 mg) and a femoral artery (10--300 mg) and intravenous infusions (10 and 20 mg/min up to 500 mg) were given. After intracoronary injection, coronary dilatation occurred for over 20 min without major changes in cardiac muscle function. Femoral vasodilatation was also induced by local injection. Slow intravenous infusion resulted in inconsistent changes of coronary blood flow. However, in one instance, coronary dilatation was observed at a plasma level of 27.8 microgram/ml, which is comparable with that reached in man after standard oral dosage. Thus, sulfinpyrazone has coronary vasodilator effects which may have relevance to patient therapy.