The effects of sub-MICs of ciprofloxacin and tobramycin on the cell surface characteristics and extracellular virulence factors of Pseudomonas cepacia were evaluated. Cells were grown in batch culture under iron-deficient and iron-replete conditions. At sub-MIC levels that did not affect bacterial growth cell surface hydrophobicity decreased under both iron-replete and iron-depleted conditions with ciprofloxacin, but increased with tobramycin under iron-sufficient conditions. Exopolysaccharide synthesis, lipase production and siderophore production were all significantly increased by the presence of ciprofloxacin under both growth conditions. Outer membrane protein and lipopolysaccharide profiles were not affected by exposure to the two antibiotics.