The effect of sodium salicylate (SA) or acetylsalicylate (ASA) on sensitivity to two different antibiotics on porin-deficient Gram-negative bacteria was investigated. Neither SA nor ASA nor any combinations of the two drugs within the therapeutic range altered minimum inhibitory concentrations (MICs) or minimum bactericidal concentrations (MBCs) of mezlocillin and ciprofloxacin against Pseudomonas aeruginosa, Serratia marcescens and Proteus vulgaris strains. It is concluded that SA and ASA do not seem to interfere with antimicrobial therapy of Gram-negative porin deficient bacteria.