Adenosine is an endogenously produced compound that has significant effects as a coronary and systemic vasodilator. Previous studies suggest that intravenous infusion of adenosine, coupled with thallium-201 scintigraphy, may have specific value as a noninvasive means of evaluating coronary artery disease. The purpose of this study was to compare the diagnostic value of adenosine thallium testing with that of standard exercise thallium testing. One hundred subjects were studied with exercise thallium imaging and thallium imaging after adenosine infusion, including 47 with angiographically proved coronary artery disease and 53 control subjects. The overall sensitivity of the thallium procedures was 81% for the exercise study and 83% for the adenosine study (p = NS); the specificity was 74% for the exercise study and 75% for the adenosine study (p = NS). The diagnostic accuracy of the exercise study was 77% and that of the adenosine study was 79%. Ninety-four percent of subjects had an adverse effect due to the adenosine infusion; however, most of these effects were mild and well tolerated. All adverse effects abated within 30 to 45 s of the termination of the study, consistent with the very brief half-life of the agent. Thus, thallium-201 scintigraphy after intravenous infusion of adenosine has a diagnostic value similar to that of exercise thallium testing for evaluation of coronary artery disease. Adenosine thallium testing may be particularly useful in evaluating patients unable to perform treadmill exercise testing.