Myocardial glucose metabolism was assessed using 18F-fluorodeoxyglucose and positron emission tomography in 6 normal volunteers, 7 patients with coronary artery disease and stable angina and 15 patients with unstable angina. All studies were carried out on resting, fasting patients. The patients were off treatment and had no evidence of acute myocardial necrosis or ischaemia. A second study investigated the myocardial glucose metabolism of 5 of the patients with unstable angina after treatment with oral nifedipine. In the first study, the metabolic rate for glucose (MRG) was found to be similar in patients with stable angina and normal volunteers (0.023 +/- 0.032 vs 0.012 +/- 0.008 mumol ml-1 min-1, P less than 0.42), whereas the MRG was significantly higher in patients with unstable angina compared with both that of normal volunteers and patients with stable angina (0.084 +/- 0.047 mumol ml-1 min-1, P less than 0.001). In the second study, the MRG of all of the 5 patients with unstable angina studied after the administration of nifedipine was significantly reduced (P less than 0.05), but was still higher than that of the normal controls. The possibility of spontaneous metabolic changes cannot be excluded, but the consistent reduction of the MRG in all 5 patients after the administration of nifedipine suggests that nifedipine has a beneficial effect on myocardial metabolism that could be related to either an increase in myocardial blood flow or to a direct metabolic effect of nifedipine.