To establish a safe and sensitive diagnostic procedure for detecting coronary vasospasm, we utilized 201-thallium myocardial SPECT combined with hyperventilation (HV-SPECT) in 29 patients with vasospastic angina (VAP) and 11 controls. Twenty-five of 29 patients with VAP and 5 of 11 controls developed transient perfusion defects on HV-SPECT, resulting in a sensitivity and specificity calculated at 86% and 55%, respectively. Overall accuracy in identifying corresponding vessels with coronary vasospasm, respectively. Coronary vasospasm tended to be identified more accurately in the left anterior descending branch and the right coronary artery than in the circumflex branch (75%, 71% and 50%, respectively). The hyperventilation test induced ischemic ECG changes in 11 of 29 patients with VAP, yielding a sensitivity of 38%. Analyzing the washout rate of HV-SPECT in patients with VAP, both the extent and severity scores of patients with ischemic ECG changes were larger than those of patients without. No serious complications occurred during HV-SPECT. In conclusion, HV-SPECT was a safe and sensitive procedure as a primary diagnostic approach for VAP. From the results of washout analysis, HV-SPECT could detect more mild myocardial ischemia than could the ECG, and seemed quite useful especially for detecting coronary vasospasm accompanied by minimal ischemic ECG changes.