The efficacy of ciprofloxacin in eradicating pharyngeal colonization of Neisseria meningitidis was studied among army recruits in Finland. Ciprofloxacin (250 mg) or placebo was given twice a day for 2 days to 118 meningococcal carriers. Meningococcal carriage was eradicated in 96% of subjects given ciprofloxacin and in 13% of those given placebos.