Glomerular T cells and monocytes in nephritis: study with monoclonal antibodies. Intraglomerular T cells, monocytes, total leucocytes and other mononuclear subsets were sought in renal biopsies from patients with glomerulonephritis, using monoclonal antibodies and immunoperoxidase techniques. Twenty–four biopsies with no significant glomerular proliferation on optical microscopy, thirty–two with only endocapillary hypercellularity, and twenty–one with extra capillary crescentic glomerular disease were studied. Few intra-glomerular leucocytes were seen in the non-proliferative group. In contrast, when compared with this group, biopsies with glomerular hypercellularity and particularly those with crescents showed increased numbers of intra-glomerular total leucocytes and monocytes/macrophages, as well as an excess of T lymphocytes and T cytotoxic/suppressor cells; T helper/inducer lymphocytes were significantly increased only in the crescentic group. Only small numbers of B lymphocytes and NK cells were found in all groups. The numbers of total glomerular T-cells and monocytes per glomerular cross section were highly correlated in the crescentic group. Only idiopathic IgA nephropathy failed to show a significant increase in the numbers of intra-glomerular leucocytes, in comparison with the nonproliferative group, Henoch–Schöenlein purpura biopsies in contrast had an excess of both monocytes and T cell subsets. The finding of T lymphocytes as well as monocytes in glomeruli of proliferative nephritis suggests that cellular immune mechanisms may play a role in their pathogenesis, especially when crescents are present.