The role of T cell-mediated immunity in the early phase of nephrotoxic serum nephritis (NTN) was examined by transfer of pan T, CD8-positive, and CD4-positive cells. The disease was induced by transferring rabbit gamma-globulin (RGG)-sensitized T cells to nude (rnu/rnu) rats pretreated with a subnephritogenic dose (a dose insufficient to cause proteinuria) of nephrotoxic serum. Mild but abnormal proteinuria was detected, and macrophages showed significant accumulation in glomeruli. Transfer of not only RGG-sensitized CD4-positive cells but also CD8-positive cells separated by the T cell markers OX8 and OX38 using the panning method caused an increased accumulation of macrophages in isolated glomeruli. No host antibody against rabbit immunoglobulins was demonstrated either in glomeruli by immunofluorescence or sera by ELISA in the early disease phase. These findings support a pathological role of T cells in initiation of glomerular injury in NTN.