We examined whether or not patients with Wegener's granulomatosis have autoantibodies against the respiratory tract and kidney, by using the direct avidin-biotin-glucose oxidase complex method. On immunostaining, the IgG fractions obtained from the sera of 2 patients with Wegener's granulomatosis and of 7 controls were coupled with biotin, and each couple was used as the primary antibody. The serum IgG sample from 1 patient with Wegener's granulomatosis definitely reacted with epithelial cells of the nasal mucosa, with the strongest reaction in basal layer. The sample from another patients with Wegener's granulomatosis showed a similar but weaker reaction. Control sera showed negative reactions in 6 subjects (3 with rheumatoid arthritis, 1 with allergic granulomatous angiitis and 2 normal volunteers) and a very weak reaction in 1 patient with poly-arteritis nodosa. These observations suggest the presence of an autoantibody reacting with some cell components of the nasal epithelium in patients with Wegener's granulomatosis.