Biofilm formed on polystyrene by 98 clinical and environmental S. maltophilia strains. Biofilm amount formed after 24 h incubation at 37°C was assessed by microtiter colorimetric assay. Strains from non-CF patients are represented by blue bars, strains from CF patients are represented by cyan bars, and strains from environmental sources (ENV) are represented by black bars. Each strain was tested in quadruplicate on two different occasions. Results were subtracted from negative control (OD492 = 0.096) and expressed as means + SDs.