Recent studies have demonstrated an important role of vascular cell adhesion molecule-1 (VCAM-1) in the pathogenesis of nephritis. In the present study, renal biopsy specimens from patients with proliferative and crescentic glomerulonephritis were subjected to immunoelectron microscopy using an anti-VCAM-1 monoclonal antibody. In control normal kidney tissue, VCAM-1 expression was restricted to the free surface of parietal epithelial cells. In diseased glomeruli, VCAM-1 was expressed on the free surface of parietal and visceral epithelial cells, on the luminal surface of capillary endothelial cells, on infiltrating monocyte/macrophage-like cells, on mesangial cells, and in the matrix of the expanded mesangium. There was also VCAM-1 expression on almost all cell types in the crescents, including macrophage-like cells, fibroblast-like cells, and epithelial cells. Some cells also showed VCAM-1 positivity in the rough endoplasmic reticulum and the perinuclear space. Both the glomerular capillary lumen and urinary spaces of Bowman's capsule contained positive reaction products, which were often associated with exocytosis by the surrounding cells. VCAM-1 was predominantly expressed on the basal and lateral surfaces of a few proximal tubules, but it could not be localized ultrastructurally. These findings suggest that production and secretion of VCAM-1 by both infiltrating monocyte/macrophages and resident glomerular cells may be related to the pathogenesis of proliferative and crescentic glomerulonephritis.