Fibrin deposition is prominent in delayed-type hypersensitivity (DTH) reactions and is initiated by antigen-specific, T-lymphocyte-directed macrophage expression of human tissue factor (HTF). To examine the role of DTH in glomerular fibrin deposition, 10 fibrin-positive and 24 fibrin-negative biopsy specimens from patients with glomerulonephritis (GN) and samples from normal controls were studied with monoclonal antibodies against T cells, macrophages, and HTF. Fibrin-positive sections showed intense glomerular staining for HTF and significantly more T cells and macrophages than fibrin-negative specimens. All the essential elements of DTH reactions can therefore be simultaneously demonstrated within glomeruli from patients with fibrin-related GN. These findings suggest a role for cell mediated immunity in GN.