Arterial fibrinoid lesions in major salivary glands and lingual minor salivary glands from four autopsied patients with primary Sjögren's syndrome were studied histologically and immunohistochemically. On a morphological basis, the preceding arterial fibrinoid necrosis was regarded as medial damage, particularly of smooth muscle cells. The medial smooth muscle cells underwent vacuolated degeneration and disappeared, and resulted in full-blown fibrinoid arteritis. By means of the immunoperoxidase method the distribution of the immunoglobulins, fibrin, complement (C3), transferrin, ferritin, vimentin and lysozyme was studied. The normal arterial wall reacted with the lambda light chain of immunoglobulin, transferrin and vimentin Vacuolated degeneration of medial smooth muscle cells, regarded as the initial change in cases of vascular fibrinoid lesion, was positive for IgG, C3 and vimentin. We suggest that IgG antibody is a useful marker to detect the initial phase of arterial fibrinoid necrosis. In the foci of fibrinoid necrosis, fibrin, C3 and vimentin were detected. Among these three antibodies, only fibrin was negative in the normal arterial wall and vacuolated degenerates of medial smooth muscle cells. Mononuclear cells surrounding areas of fibrinoid necrosis stained strongly with antisera to immunoglobulins, transferrin, ferritin and vimentin, and negatively with fibrin, C3 and lysozyme antibodies.