A clinical evaluation of the dipyridamole in the myocardial perfusional scintigraphy (MPS) was carried out in a series of patients, comprehensive of cases of unstable angina, aiming to assess the feasibility and diagnostic validity of the test and to state its possible role in comparison with exercise stress test. On the whole, 107 subjects were examined (34 with stable angina, 23 with unstable angina, 19 with recent myocardial infarction, 15 with atypical angina, 10 with chest pain of uncertain origin and 6 healthy volunteers), performing 108 scintigraphic studies (48 after dipyridamole infusion and 37 after bicycle exercise). In the studies with physical or pharmacologic stress a redistribution scintigraphy was also performed (4 hour after the injection). The dipyridamole stress test was well tolerated by patients with unstable angina too and showed a diagnostic sensitivity equivalent to that with exercise stress, although the latter appears better as regards image quality and can give an increase of sensitivity provided electrocardiographic findings are evaluated. Post-stress redistribution of 201 Tl in delayed scans was shown either after dipyridamole or after exercise in patients with typical angina without prior infarction. The computation, by the Bayes's theorem, of the predictive value of the two tests leads the Authors to the following conclusions: in atypical angina (prevalence of CAD: about 40%) the association MPS + exercise ECG is preferable; in patients with chest pain of uncertain origin or with asymptomatic electrocardiographic alterations (prevalence of CAD: about 15%) it is better to take into account only the scintigraphic findings obtained after exercise or pharmacologic stress, to avoid an excess of false positive results.