By use of the tlc overlay procedure we have shown that exoenzyme S extracted from cultures of Pseudomonas aeruginosa specifically binds to the glycolipids asialoGM1, asialoGM2 and to a lesser extent lactosyl ceramide. More significantly, strong binding was also observed to the glycerolipid receptor we have detected for Helicobacter pylori (Lancet ii, 238-241.1989). Exoenzyme S can be extracted in a toxic and nontoxic form. Toxicity correlated with ability to bind the H. pylori receptor. This species was the only receptor detected in the most sensitive cell lines. The relative binding of exoenzyme S to the ganglio series glycolipids and the glycerolipid receptor was modified in a reciprocal manner in the presence of metal ions, suggesting that exoenzyme S has two interrelated receptor binding sites.