The purpose of the study was to investigate the adhesion of Pseudomonas aeruginosa strains with varying pathogenic potential to purified ocular mucin. Bovine conjunctival mucin was purified by three sequential density gradient centrifugation steps. Immobilised mucin was probed with biotin-labelled bacteria isolated from different contact lens events and quantified by densitometry. Bacterial pili were identified by electron microscopy. The results indicate that purified ocular mucin consisted of a polydisperse high molecular weight population containing at least one species of goblet cell origin and was associated with a 97 kDa mucin-associated protein. Three pathogenic P. aeruginosa strains, Paer1 (57.5 +/- 10.8x10(6) CFU ml(-1); contact lens induced acute red eye (CLARE)), 6294 (127.0 +/- 4.7x10(6) CFU ml(-1); microbial keratitis) and Paer25 (60.5 +/- 11.3x10(6) CFU ml(-1); CLARE) exhibited a significantly higher level of adhesion to mucin than the negative control, E. coli (14.3 +/- 9.6x10(6) CFU ml(-1)) (p<0.005). The remaining P. aeruginosa isolates, Paer3 (asymptomatic patient), Paer12 (microbial keratitis) and ATCC 15442 (standard environmental strain) did not significantly differ in their mucin adhesion from the negative control. The majority of bacterial strains tested contained pili; thus differences in mucin adhesion observed could not be solely explained by pili status. In conclusion, P. aeruginosa isolates exhibit differential adhesion patterns to purified ocular mucin. It is proposed that more avid mucin-adhering strains are given the opportunity to adhere and subsequently penetrate the mucous layer of the tear film to initiate pathogenesis.