In 60 patients with angiographically documented 2- or 3-vessel disease (at least 70%) thallium-201 images after dipyridamole (0.50 mg/kg bodyweight i.v.) and 4 h later were obtained. In 95% of the patients stress perfusion defects were found. In 48% of the cases scintigraphy correctly diagnosed the presence of multivessel disease, but in only 30% of the patients were all angiographically narrowed vessels detected. The reliability of the method was much higher in the detection of 'infarct stenoses' (96%) than of 'noninfarct stenoses' (46%). The regional sensitivity to assess stenoses of the left anterior descending artery (75%) and right coronary artery (73%) was greater than in stenoses of the left circumflex artery (37%). Thallium-201 scintigraphy after dipyridamole is a sensitive method for diagnosing the presence of coronary artery disease. The diagnostic value is severely limited however by the fact that coronary vasodilation may provoke perfusion abnormalities only in the most ischemic regions, whereas perfusion defects in other areas may not be detectable. Therefore this method does not allow the precise quantitation of all coronary stenoses in the majority of patients.