The response to prolonged hyperventilation (HVT) was evaluated by electrocardiography (HVT-ECG) and thallium-201 myocardial scintigraphy (HVT-Tl-Sc) in 40 patients suspected of vasospastic angina. Both tests showed ischaemic changes in 16 patients and no changes in 20 patients. Two patients had abnormal HVT-ECG and normal HVT-Tl-Sc, and the reverse combination was found in two patients. Prolonged HVT was performed in 14 patients during coronary angiography (CAG). Nine developed transient total or subtotal occlusion in one of the major coronary arteries, all of whom had ischaemic HVT-ECG and eight had abnormal HVT-Tl-Sc. In the five patients without spasm at CAG four had normal HVT-ECG and all five normal HVT-Tl-Sc. Our data suggest that HVT-ECG and HVT-Tl-Sc have essentially the same sensitivity and specificity in detecting vasospastic angina.