The effects of sodium deoxycholate, tobramycin and amiloride on the inhibitory effect (minimum inhibitory concentration) of ciprofloxacin againstPseudomonas aeruginosa(strain PAO 511 and two clinical isolates, one from a burn infection and the other from a cystic fibrosis respiratory tract infection) were examinedin vitro.The method used was a macrodilution technique in Mueller‐Hinton broth at 37C. Marked enhancement of ciprofloxacin activity was observed in the presence of 4.15mg/ml sodium deoxycholate, 0.4μg/ml tobramycin and 50μg/ml amiloride. It is suggested that these observations may be clinically important in the treatment of localisedPseudomonas aeruginosainfections, eg, within the respiratory tract of cystic fibrosis patie