The incremental diagnostic yield of exercise 201Tl scintigraphy with visual and quantitative analysis was determined in 191 patients with known or suspected coronary artery disease (CAD). The coronary arteriogram was used as the gold standard. After pre-test clinical and exercise electrocardiographic data were taken into consideration, scintigraphy was found to have additional diagnostic value both in the diagnosis of CAD and of multivessel disease, with quantitative analysis being superior to visual analysis. The impact of 201Tl scintigraphy on the patient's treatment--conservative treatment versus revascularization--was also evaluated. The impact was relatively low, as the decision for revascularization was based primarily on the angiographic result and the severity of the anginal pain. This result reflects only the decision making process used in our clinic and permits no conclusion to be made concerning the possible value of 201Tl scintigraphy in this type of medical decision making process.