During the past 2 years, 102 patients were treated for unstable angina pectoris (AP) in our department. Fifteen of them had recurrent chest pain at rest despite treatment with various anti-anginal agents, or prolonged chest pain unresponsive to sublingual nitroglycerin; they received intravenous isosorbide dinitrate (ISDN) infusion . A rapid bolus injection of 2 to 6 mg followed by an infusion of 2 to 5 mg/hr was given to 10 patients with acute chest pain, and 5 patients who were free of chest pain at the time, but had repeated episodes of angina in the past 24 hours, were given ISDN infusion without a bolus injection. Chest pain disappeared completely in 13 patients, but recurred in 2 of them when the does was tapered. Tow other patients experienced recurrent chest pain during ISDN infusion, and additional boluses were given. the hospital course was uneventful in 11 patients. Four patients who had recurrent anginal attacks underwent emergency coronary cineangiography under intraaortic ballon counterpulsation and aorto-coronary bypass surgery. There were no hospital deaths, no one had subsequent acute myocardial infarctions, and only 2 patients had mild to moderate headache as a side effect. Although the patient population is small, intravenous ISDN infusion is useful in the management of severe unstable AP.