The aim of the present study was to evaluate the yield of radionuclide studies for the diagnosis of coronary artery disease (coronary artery narrowing greater than 50%) in a prospective series of 73 patients with thoracic pain and equivocal electrocardiographic stress testing. In the study population, the prevalence of coronary artery disease was 51%. The sensitivity, specificity, diagnostic accuracy and the post-test probability difference curves according to the Bayes' theorem were calculated for 201-thallium exercise testing and radionuclide exercise equilibrium ventriculography. For the latter study the following criteria were considered: (1) increase in left ventricular ejection fraction less than 5%; (2) the criterion proposed by Rozanski; (3) decrease in regional ejection fraction; and (4) abnormalities in phase and amplitude analysis (Fourier). 201-thallium exercise testing was the most sensitive (97%) and accurate (86%) study. Radionuclide ventriculography sensitivity was always lower for any criterion, although its best result was for evaluation of regional ejection fraction (85%). The most specific study was Fourier analysis (97%), although its sensitivity was low (42%). The application of Bayes' theorem to these results shows that the highest post-test probability difference values were achieved with 201-thallium exercise testing for prevalences higher than 40% and with Fourier analysis for lower prevalences.