The specificity and binding capacity of the galactophilic lectin from the Gram negative bacterium Pseudomonas aeruginosa (PA-IL) was determined by solid phase measurements using galactosylated neoglycoproteins immobilized on microtiter plates. The bacterial lectin reacted with both short chain ( monosaccharide) and long chain ( pentasaccharide) glycoconjugates. Among the Gal alpha 1-XGal disaccharides, the highest affinity was observed towards the Gal alpha 1-3Gal structure. Raising the incubation temperature enhanced the lectin-polysaccharide agglutination, and it is suggested that binding to certain conformations of polysaccharides could vary between lectins with the same monocarbohydrate specificity and that this activity may, in part, be temperature dependent. Histochemical examination of lectin binding to different porcine tissues suggests a differential glycosylation of the carbohydrate antigens on endothelial cells in various parts of the vascular system. In the pancreas, PA-IL also adhered to the excretory ducts. These observations on PA-IL binding could be of importance both to determine infection foci in P. aeruginosa- mediated vacuities and to determine its role for pancreatic involvement in cystic fibrosis.