Fimbriae (pili) on the surface of bacteria have been suggested to facilitate adherence to mucosal epithelial surfaces. Three Pseudomonas cepacia cystic fibrosis isolates were screened for their ability to agglutinate erythrocytes (HA), a characteristic of some fimbrial types. One strain, designated PC103, was HA+, while another, PC109, was HA-. A fimbriated (f+) HA+ derivative of PC109 (PC2(13)) was selected by repeated erythrocyte adsorption. The two HA+ strains were shown by transmission electron microscopy to possess fimbriae which averaged 4.8 +/- 1.36 nm in width and 200 to greater than 2,100 nm in length (PCE2(13)) and 3.4 to 11.4 nm in diameter and 280 to 720 nm in length (PC103). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of outer membrane proteins prepared from PC103, PC109, and PCE2(13) indicated that the putative fimbrial subunit had a mass of 16 kDa. Western blot (immunoblot) analysis of sheared cell supernatants indicated that the 16-kDa subunit from PC103 and PCE2(13) reacted with antibody to the P. aeruginosa PAK pilin subunit. Southern blot analysis of a SalI digest of PC103 DNA showed DNA fragments which hybridized to P. aeruginosa PAK probes containing either the pilin structural gene (pilA) or the pilin accessory genes (pilB, -C, and -D) but not the conserved N-terminal region of pilA. A 15-kb band was common to both hybridizations, indicating that this fragment contains the PC103 fimbrial gene cluster. These results indicated the presence of homology between P. aeruginosa PAK and PC103 fimbriae but also suggested that the P. cepacia fimbriae are not type IV-like. The importance of fimbriae in adherence to A549 cells (type II pneumocytes) was assessed with PC109 (f-) and PCE2(13) (f+). PCE2(13) had an approximately 20-fold-higher level of adherence to A549 cells than PC109. This suggested that fimbriation of P. cepacia is associated with increased adherence in vitro.