The lung uptake of thallium-201 (201Tl) in planar imaging was evaluated in 384 patients enrolled in the SIRT study (Italian Multicentre Study on Thallium Reinjection). All patients underwent treadmill exercise, and at peak exercise 74 MBq of 201TI were injected. The patients were then evaluated after reinjection of 201Tl under baseline conditions. The left ventricle was subdivided into 16 echocardiographic and 15 scintigraphic segments. The best correlates of visually scored 201Tl lung uptake, of the lung heart ratio and lung wash-out were checked. The independent variables entered in the stepwise multiple-regression analysis were: the echocardiographic wall motion index, the scintigraphic perfusion score index, and the number of segments that improved by at least 1 and 2 grades after redistribution and after reinjection. We concluded that the lung:heart ratio and, in particular, lung wash-out do not correlate more closely than the visual score with the variables taken into consideration. This suggests that visually scored lung uptake of 201Tl is still of value in nuclear cardiology practice. The scintigraphic variables associated with reinjection do not seem to offer any additional information with respect to redistribution variables. We also analysed the impact on 201Tl lung uptake of several other index variables. Student's t-test revealed that no single variable significantly alters lung uptake after stress testing.