The purpose of this study was to determine the frequency of pulmonary embolism in patients admitted with acute chest pain but without myocardial infarction (non-AMI patients). We examined 175 consecutive non-AMI patients without unstable angina pectoris within the first 48 h of admission. The patients were first examined by perfusion pulmonary scintigraphy. If the scintigraphy was abnormal, it was combined with a <sup>81m</sup>Kr ventilation scintigraphy. Perfusion scintigraphy was abnormal in 21 patients, and the subsequent combined perfusion/ventilation scintigraphy was used to identify 5 patients (2.5%) who had a high probability for pulmonary embolism, which was not clinically suspected at the time of admission. Three of these 5 patients had a decreased arterial oxygen tension upon admission, and 3 had abnormalities in their electrocardiogram. Pulmonary embolism only occurred in 2.5% of the non-AMI patients. The prognosis of untreated patients, however, is markedly worse as compared with treated patients. We, therefore, suggest that pulmonary scintigraphy be performed in non-AMI patients who have uncharacteristic electrocardiographic changes and/or a low arterial partial oxygen tension when no other abnormality has been found within 24 h of admission.