The opportunistic pathogen Pseudomonas aeruginosa contains lectins of which one of them, PA-IL (gene lecA), shows preference for alpha-galactosylated glycans. The bacterial lectin is probably important in the carbohydrate-mediated adhesion of the microorganism to endothelia and epithelia and thereby the lectin facilitates entering and damaging of the cells. The requirements for the interaction between PA-IL and the carbohydrate epitopes to which the bacterial lectin may bind were here Studied using alpha-galactosylated neoglycoproteins that were immobilized on Microtiter plates. It is concluded that the carbohydrate recognizing site of the lectin can have a binding requirement of only one saccharide. Lectin histochemistry was performed on sections from wild type mice and from knock-out mice, which lack function of the alpha.1,3-galactosyltransferase gene. All assays with the P. aeruginosa lectin were compared with the results obtained using an isolectin from the legume shrub Griffonia simplicifolia: the GSI-134 isolectin, which is highly specific for glycans terminating in Ga1 alpha 1-R. In the wild-type mice, lectin histochemistry showed a strong capillary reaction in heart, kidney and adrenal gland while none of the two lectins were able to detect capillaries in the pancreas. This could indicate a differential glycosylation with respect to endothelial cell Gal alpha. epitopes among different organs. Further, since no PA-IL bindingto the endothelial cells in the KO mouse was observed, it seems that, in the mouse, the Pseudomonas lectin adheres to the Gal alpha l-3Ga4 beta 1-G1cNAc carbohydrate on endothelial cells in most organs and tissues. Finally, lectin staining of the basement membrane of the acini in the exocrine pancreas suggests the presence of Ga1 alpha 1-3Gal epitopes in WT mice basement membranes that are not detected by the P.aeruginoso lectin.