Biopsies from 46 kidneys that were subsequently transplanted were examined with monoclonal antibodies and the peroxidase-antiperoxidase technique to localize HLA-ABC and DR antigens. There was no variation in the expression of HLA-ABC which was present on all cells of the renal parenchyma. HLA-DR was found consistently on the endothelium of glomeruli and of intertubular capillaries but was only weakly expressed, or not expressed at all, on the endothelium of large vessels. The mesangium of glomeruli also stained for HLA-DR. But there was a striking variation in the expression of HLA-DR by proximal renal tubular cells in the 46 kidneys. HLA-DR was absent from tubules in 11 of 46 kidneys (23%) and probably absent or very weakly expressed in a further 8 kidneys (17%). The expression of HLA-DR in tubular epithelium was not related to the donor's age, sex, blood group, or ischemia times. However, the frequency of HLA-DR3 increased (55%) in donors of kidneys with tubular DR-negative kidneys, as compared with a frequency of 15% in donors of tubular DR-positive kidneys. Although this difference was not significant after a correction for the number of comparisons made, it suggests a genetic influence on the expression of tubular DR. The survival of tubular DR-negative kidneys was better at 1 year than that of tubular DR-positive kidneys (70% vs. 57%--not significant), and tubular DR-positive grafts may have had a higher rate of delayed function when transplanted in cases with a donor-specific positive B cell crossmatch. There was no obvious variation in the number of dendritic cells stained with antibodies to HLA-DR and the leukocyte common antigen despite prior administration of high doses of steroids to some donors before nephrectomy.