We studied the value of exercise thallium-201 (Tl-201) scintigraphy for evaluation of myocardial perfusion improvement and the detection of restenosis in patients after successful percutaneous transluminal coronary angioplasty (PTCA). Fifty-three patients (43 male and 10 female) ages 38-71 years (mean 55.3) were analysed. Exercise Tl-201 scintigraphy was performed before PTCA, and 6-10 days and then 3-6 months after the procedure. In all patients repeated coronary angiography was done 3-6 months after PTCA. Before PTCA myocardial perfusion defects were observed in all patients. Immediately after PTCA, an improvement in myocardial perfusion was noted in 36 patients (61%). Total normalisation of the scintigraphic picture was observed in only 12 patients. Coronary angiography after 3-6 months showed patency of dilated vessels in 11 out of those 12 patients (91.3%). In scintigraphy, performed 3-6 months after PTCA, a normal scan was present in 20 patients and recurrence of stenosis was found in only 2 of those 20. Stenosis was found in 22 (60%) of 33 patients with perfusion defects. For the purpose of describing the character of the myocardial perfusion changes, statistical analysis of a number of segments was performed. The predictive value of Tl-201 scintigraphy for detection of restenosis was established. The positive value for the procedure performed 6-10 days after PTCA was 56%, and the negative value of prediction of restenosis was 91%. Three to 6 months after PTCA, a high negative value of scintigraphy was observed (-90%) and a low positive predictive value was still present (63%).