Although mononuclear phagocytes were once considered the sole source of tumor necrosis factor alpha (TNF), it is now understood that other cell types, including T and B lymphocytes, may be stimulated to produce this factor. Herein we describe the release of a cytotoxic activity in vitro by isolated rat glomeruli and cultured glomerular mesangial cells. Immunoperoxidase staining with monoclonal antibodies against Ia and leukocyte common antigen-documented cultured mesangial cell populations were free of mononuclear phagocytes. Cytotoxic activities generated by isolated glomeruli and mesangial cell cultures eluted on gel chromatography in two peaks corresponding to molecular weights of 17 and 40 kDa and were fully inhibitable by anti-recombinant murine TNF antiserum. These data strongly suggest that intrinsic glomerular mesangial cells contribute to TNF release by intact glomeruli. Intraglomerular generation of TNF and perhaps other cell types may bear upon the pathogenesis of immune glomerular injury.