The in vitro activity of 17 commercially manufactured disinfectants routinely used in a large teaching hospital was tested against 128 strains of Pseudomonas aeruginosa isolated from hospitalized patients and the hospital environment. Except for quaternary ammonium salts, all the disinfectants at dilutions higher or equalling those recommended by the manufacturer were adequate to suppress P. aeruginosa. Chlorhexidine-, povidone-iodine- and glutaraldehyde-based disinfectants at dilutions 4 to 8-fold lower than the normal use dilution had a marked bactericidal effect ( > 3 log10 reduction of viable cells) within a short time (10 to 120 min). Similar formulations produced by different manufacturers exhibited comparable activity against P. aeruginosa.