Tumor necrosis factor alpha (TNF alpha) and interleukin-6 (IL-6) antigenic sites were shown within the resident glomerular mesangial cells of lupus nephritis patients applying the colloidal gold immunocytochemical approach at the electron microscopic level. Using specific polyclonal antibodies against human recombinant (hr) TNF alpha and hrIL-6 in conjunction with the protein A-gold complex, TNF alpha and IL-6 were shown in the mesangial cells, being particularly associated with the membranes of the rough endoplasmic reticulum. In addition, IL-6 also was present in glomerular immune deposits and occasionally in glomerular epithelial cells. In normal renal tissue the TNF alpha and IL-6 immunoreactivities were undetectable. The specific presence of TNF alpha and IL-6 in pathological specimens was shown by several control experiments. Thus, our results offered morphological support that TNF alpha and IL-6 might play a role in human lupus nephritis. The data showed their synthesis by the mesangial cells and their possible participation in the progression to chronicity of the renal injury on secretion.