AbstractThe binding of a panel of blood group‐reactive lectins to frozen sections of human kidney was studied with a special emphasis on reactivity with endothelia and basement membranes. The blood group A‐reactive lectins, all specific for α‐D‐N‐acetylgalactosamine (GalNAc),Helix aspersa(HAA),Helix pomatia(HPA), andGriffonia simplicifoliaI‐A4(GSA‐I‐A4) agglutinins bound to the endothelium in specimens with blood groups A and AB. In other samples, these lectins reacted predominantly with tubular basement membranes, as well as with certain tubules. BothDolichos biflorus(DBA) andVicia villosaagglutinins (VVA), reported to react with blood group A1substance, failed to reveal endothelia in most specimens, but bound differently to tubules in all blood groups. The blood group B‐reactive lectins, specific for α‐D‐galactose (α‐Gal) or GalNAc, respectively, GSA‐I‐B4andSophora japonicaagglutinin (SJA), bound to the endothelia in specimens from blood group B or AB and in other specimens bound only to certain tubules. Among the blood group O‐reactive lectins, specific for α‐L‐fucose (Fuc),Ulex europaeusI agglutinin (UEA‐I) conjugates, but not other lectins with a similar nominal specificity, bound strongly to endothelia in specimens with blood group O. The UEA‐I conjugates bound distinctly more faintly to endothelia in specimens of other blood groups. The present results indicate that lectins, binding to defined blood group determinants, react with endothelia in specimens of the respective blood group status. Furthermore, they suggest that basement membranes and some tubules in the human kidney show a distinct heterogeneity in their expression of saccharide resi