A study was undertaken to evaluate the role of positive infarct scintigraphy in the diagnosis of acute myocardial infarction (AMI), using Technetium99m stannous pyrophosphate (Tc-PYP) and a portable gamma camera. Sixty-one patients admitted to the Coronary Care Unit (CCU) with a presumptive diagnosis of AMI or ischaemic cardiac pain were studied. Positive scans were present in 24/25 (96%) patients with AMI and new Q waves, and in 10/12 (83%) patients with AMI and no Q waves. Nine of eleven (82%) patients with chest pain and no infarction had negative scans. Of thirteen patients with unstable angina, ten (77%) had positive scans. A further eight patients undergoing coronary artery bypass surgery for angina pectoris were studied pre- and postoperatively. Two patients had strongly positive postoperative scans. The Tc-PYP scan is valuable in the detection of peri-operative infarction following coronary artery surgery, and in patients with unstable angina the technique may detect small amounts of myocardial necrosis undetectable by more conventional means. When the diagnosis of infarction is obvious from the ECG, enzymes, or a combination of the two, the Tc-PYP scan provides no extra information helpful in patient management.