The aim of the study was to evaluate the validity of 201Tl scanning for clinical routine use in the diagnosis of coronary heart disease. A computer-aided matrix with very high resolution displaying subtle color nuances was used. For semi-quantitative assessment a scale with 16 colors was applied. This permitted to differentiate between changes of intensity of 6.25%. Compared with the ECG on exercise no higher sensitivity or specifity of 201Tl scanning was found using coronary angiography as the reference method. When a typical angina pectoris and a pathological ECG on exercise was present, confirmation of the diagnosis of coronary heart disease by scanning was readily obtained. Moreover, in the event of equivocal findings in the ECG and of atypical chest pain scanning is helpful without having to resort to invasive methods. Additionally to the exercise ECG, the location of ischemic areas in the myocardium can be easily demonstrated by scanning. When angiography has shown unobstructed coronary arteries but the ECG is suggestive of scar formation, scintigraphy provides additional information regarding the diagnosis of coronary heart disease. It is also possible by scanning to delineate the tissue defect representing fibrotic areas. This is necessary for instance when aneurysmectomy is planned.