Of 18 patients with Takayasus arteritis who underwent 99mTc-MAA (macroaggregated albumin) perfusion luing seanning, 9 (50%) showed perfusion defects. Chest X-rays of them were nonspecific. One patient underwent ""Tc-DTPA radioaerosoJ inhaIation lung scanning simultaneously, which revealed normal. So routine sr.reening radioisotope perfusion lung scanning is helpful to evaluate pulmonary arterial involnmement in Takayasu's arteritis patients. And Takayasus arteritis should be included in differential diagnosis of pulmonary embolism.