To study the incidence of right ventricular infarction and the effect of intracoronary thrombolysis on the ischaemic right ventricular myocardium, we performed intracoronary myocardial thallium scintigraphy in 18 patients with complete occlusion of the right coronary artery who underwent intracoronary thrombolysis. In 15 of these patients, intracoronary thallium-201 and technetium-99 m pyrophosphate scintigrams were performed simultaneously. All 18 patients had a right ventricular thallium defect before thrombolysis, and all had new thallium uptake after thrombolysis. 17 out of 18 patients had a left ventricular thallium defect before thrombolysis, but only 10 of them showed new thallium uptake after thrombolysis. 14 out of 15 patients had a left ventricular technetium-99 m pyrophosphate spot after thrombolysis and some diffuse pyrophosphate accumulation in the area of the right ventricle. In one patient pyrophosphate accumulation was found only in the area of the right ventricle. Thus, right ventricular thallium defects were detected by intracoronary thallium scintigraphy in the majority of patients with inferior acute myocardial infarction due to right coronary artery occlusion. Right ventricular thallium defects were always reversible in contrast to left ventricular thallium defects in the same patients, suggesting that right ventricular myocardium tolerates ischaemia better than left ventricular myocardium.