In seven patients with vasospastic angina, a transient myocardial perfusion defect was demonstrated on Tl-201 myocardial imaging after hyperventilation (HV). The development of spasm on one or more coronary arteries after HV was confirmed by later coronary arteriographic studies, with the perfusing area of the coronary arteries being compatible with the scintigraphic location of the defect. Repeated 12-lead electrocardiograms failed to establish the diagnosis in one of the seven patients. It is concluded that HV Tl-201 myocardial imaging provides invaluable information in establishing a diagnosis of vasospastic angina.