A 48-year-old man presented to hospital with prolonged ischaemic chest pain. No electrocardiographic or enzymic changes of acute myocardial infarction were found. Angiography performed five days later showed 75% luminal narrowing of the proximal left anterior descending (LAD) coronary artery, but no other significant abnormality. On the following day, he developed an acute anterior myocardial infarct. On repeat angiography, undertaken within 2 1/2 hours of the onset of symptoms, the LAD was found to be totally occluded. A guidewire was immediately passed through the occlusion, and streptokinase was infused through the left coronary artery for approximately 30 minutes. The vessel became patent immediately after the insertion of the guidewire, and remained so during the infusion of streptokinase. Coronary artery bypass graft surgery was successfully undertaken after the completion of the procedure.