The fluoroquinolone trovafloxacin was bactericidal (0.47 +/- 0.23 Delta log(10) CFU/ml h after 10 mg/kg of body weight and 0.78 +/- 0.15 Delta log(10) CFU/ml h after 30 mg/kg) in the treatment of experimental meningitis caused by a highly penicillin-resistant (MlC and minimum bactericidal concentration = 4 and 4 mu g/ml) strain of Streptococcus pneumoniae. Combinations with ampicillin and rifampin were indifferent compared to single drugs.