Pili have been demonstrated to be the adhesins of nonmucoid Pseudomonas aeruginosa for buccal cells. In this study, we examined their role in the adherence of both mucoid and nonmucoid strains to injured tracheal cells. Pili incubated with tracheal cells inhibited the adherence of a nonmucoid strain in a dose-dependent manner. Both homologous and heterologous pili inhibited this nonmucoid strain. Antibody against pili from the nonmucoid strain inhibited adherence of the homologous but not a heterologous strain. Pili failed to inhibit two mucoid strains, but inhibited nonmucoid variants derived from mucoid strains. These studies suggest that pili mediate the adherence of nonmucoid strains to injured tracheal cells but that they are not the final mediators of adherence of mucoid strains. It is also inferred that there are differences in the receptor for mucoid and nonmucoid strains.