The effects of nifedipine, a potent calcium antagonist, were studied in patients with unstable angina, coronary spasm and myocardial ischemia. Data from two separate groups of patients studied in the cardiac catheterization laboratory indicate that intracoronary injection of nifedipine promptly reversed coronary spasm--whether provoked or spontaneous--in five of six patients. In other patients, direct intracoronary injection of the drug was compared with intravenous administration. After intracoronary injection, local mechanical cardiac action virtually ceased, and the ventricular wall became thinner during systole. Thus, a specific inhibitory action on contractile energy expenditure could be demonstrated in the presence of increased coronary flow. This "oxygen-sparing" effect was tested in a group of 31 patients with symptomatic unstable angina whose pain at rest, with ST-T changes, had not responded to 8 hours of treatment with maximal beta adrenergic blockade, nitrates and bed rest. The addition of 6 X 10 mg of nifedipine rendered 27 of these patients asymptomatic within 1.5 hours. In the four patients who did not respond, coronary arteriography demonstrated severely stenotic lesions. Two of the four patients subsequently responded to intraaortic balloon pumping and bypass surgery; one patient had a myocardial infarction and one who had a 90 percent reduction in the diameter of the left main coronary artery, died. It is concluded that nifedipine should be added to beta adrenergic blockade therapy if the latter does not appear to be immediately effective. This combination has not been shown to cause any hemodynamic deterioration, and only a minority of the patients treated sustained a myocardial infarction during the first 3 months of follow-up. The use of nifedipine in unstable angina deserves further clinical evaluation.