Intravenous dipyridamole thallium testing is a useful alternative procedure for assessing coronary artery disease (CAD) in patients who are unable to perform maximal exercise tests. Ischaemic ST segment depression and angina pectoris are frequently observed during the test, in particular when exercise is added to dipyridamole infusion. To establish the clinical significance and additional diagnostic value of these markers of ischaemia during dipyridamole low-level exercise testing (DXT) 57 patients with CAD (group A), 21 patients with normal or near-normal coronary arteries at coronary arteriography (group B), and 20 healthy subjects with low likelihood of CAD (group C) were studied. During DXT ischaemic ST segment depression was observed in 28 patients (47%) of group A and in two patients (10%) of group B. Angina pectoris was experienced by 35 patients (61%) of group A and by five patients (24%) of group B. The positive predictive value of both ST depression and angina pectoris was high (88 and 93%, respectively), but the negative predictive values were low (42 and 40%, respectively). Combining ST segment analysis with the findings of thallium imaging significantly increased the diagnostic accuracy of the test. ST segment depression, angina pectoris, and thallium abnormalities were highly specific findings if the study population consisted of asymptomatic subjects with a low likelihood of CAD (group C). Sensitivity for the detection of the presence of CAD increased with the extent of CAD for all parameters studied. Thus, ST depression and angina pectoris, alone or in combination, during DXT have little diagnostic significance, although sensitivity is increased in patients with triple-vessel CAD.(ABSTRACT TRUNCATED AT 250 WORDS)