Monoclonal antibodies to human monomorphic class I and class II major histocompatibility complex (MHC) determinants have been used with immunofluorescence and immunoperoxidase techniques, to localize these an- tigens in normal human kidneys. HLA-DR antigen was located in the glomeruli (probably on endothelium as well as in the mesangium) and within the cells of cortical and medullary tubules. Dendritic cells in the renal inter- stitium stained brightly for the DR antigen and could be distinguished from the staining of capillary endothelium. The vascular endothelium of large vessels stained less densely for the HLA-DR antigen than for HLA-ABC an- tigens. The glomeruli stained intensely for the HLA-ABC antigens and diffuse staining of HLA-ABC antigens was also noted within renal tubular cells.