To evaluate the accuracy of single dose thallium scanning (SDTS) utilizing exercise and four-hour redistribution images, 106 patients were evaluated; 91 had a >50 percent stenosis of at least one major vessel, 15 had no significant disease. Ischemia: compared to simultaneous ECG exercise tolerance test, SDTS was 86 percent vs 48 percent sensitive (P < 0.01), 100 percent vs 80 percent specific and 100 percent vs 94 percent predictive. Infarction: 79 percent of patients with >50 percent stenoses had persistently decreased perfusion on redistribution scanning compared to 43 percent with ECG Q waves (P < 0.01). Abnormally contracting segments: persistently decreased perfusion on redistribution scanning was 73 percent sensitive in the identification of abnormally contracting segments on left ventriculography compared to 33 percent by ECG Q waves (P < 0.01). Coronary artery disease: compared to exercise tolerance test and ECG Q waves, exercise and redistribution thallium scanning was 91 percent vs 71 percent sensitive (P < 0.01), 87 percent vs 73 percent specific and 98 percent vs 94 percent predictive in the detection of coronary artery disease. In conclusion, SDTS is significantly more sensitive than standard exercise tolerance testing and ECG parameters in the diagnosis of ischemia and the detection of patients with coronary artery disease and abnormally contracting segments and offers an alternative to conventional double-dose exercise and rest 201thallium scanning. To evaluate the accuracy of single dose thallium scanning (SDTS) utilizing exercise and four-hour redistribution images, 106 patients were evaluated; 91 had a >50 percent stenosis of at least one major vessel, 15 had no significant disease. Ischemia: compared to simultaneous ECG exercise tolerance test, SDTS was 86 percent vs 48 percent sensitive (P < 0.01), 100 percent vs 80 percent specific and 100 percent vs 94 percent predictive. Infarction: 79 percent of patients with >50 percent stenoses had persistently decreased perfusion on redistribution scanning compared to 43 percent with ECG Q waves (P < 0.01). Abnormally contracting segments: persistently decreased perfusion on redistribution scanning was 73 percent sensitive in the identification of abnormally contracting segments on left ventriculography compared to 33 percent by ECG Q waves (P < 0.01). Coronary artery disease: compared to exercise tolerance test and ECG Q waves, exercise and redistribution thallium scanning was 91 percent vs 71 percent sensitive (P < 0.01), 87 percent vs 73 percent specific and 98 percent vs 94 percent predictive in the detection of coronary artery disease. In conclusion, SDTS is significantly more sensitive than standard exercise tolerance testing and ECG parameters in the diagnosis of ischemia and the detection of patients with coronary artery disease and abnormally contracting segments and offers an alternative to conventional double-dose exercise and rest 201thallium scanning.