Pseudomonas aeruginosa expresses two lectins which are implicated in adhesion and biofilm formation. In this study, we demonstrate that P. aeruginosa LecB is involved in pilus biogenesis and proteolytic activity. Moreover, neither lectin was involved in adhesion to human tracheobronchial mucin. We infer that some of the ascribed functions are secondary effects on other systems rather than effects of the lectins themselves.