Regression of the left main trunk lesion by steroid administration in Takayasu's aortitis. A 62-year-old man with unstable angina due to severe narrowing of the left main trunk (LMT) was examined. Emergency bypass surgery was performed with an internal mammary artery graft, instead of a saphenous vein graft, because of the thickened, edematous ascending aorta. Postoperative coronary angiography showed the lesion of the LMT markedly regressing. Presumably, this stenotic lesion of the LMT was caused by active aortitis and was partially reversible by steroid administration both during and after surgery. Steroid therapy can be added to the list of treatments for cases of LMT disease associated with Takayasu's aortitis, if signs of active inflammation are present. 