Thirty one patients were treated with oral ciprofloxacin for bronchitis with Pseudomonas aeruginosa. Twenty eight patients had permanent and 14 transient risk factors. Nine patients had a hospital infection with Pseudomonas aeruginosa. Sixteen patients were cured, complete or partial, but Pseudomonas aeruginosa persisted or recurred in 19 patients. Patients with hospital infection did better than other patients. There was a significant decrease in in vitro susceptibility of persisting strains of Pseudomonas aeruginosa to ciprofloxacin and a tendency of recovery of susceptibility for the drug after treatment.