The activity of five antibiotics was tested against 82 isolates of Legionella pneumophila obtained from water systems in nine European countries. All isolates were susceptible to clarithromycin (MICs 0. 03-0.5 mg/L), erythromycin (MICs 0.125-2.0 mg/L), ciprofloxacin (MICs 0.06-0.25 mg/L), pefloxacin (MICs 0.06-0.5 mg/L) and rifampicin (MICs < or = 0.007-0.015 mg/L). It seems that antibiotics used for legionellosis continue to exhibit good activity against L. pneumophila isolates from environmental sources in European countries.