The in-vitro activity of trovafloxacin and nine other antimicrobials was determined for 413 non copy anaerobic clinical isolates. Trovafloxacin was the most active quinolone tested with an MIC90 of 0.5 mg/L against Gram-positive cocci (n = 75); MIC90 of 4 mg/L against Gram-positive bacilli (n = 151); MIC90 of 0.5 mg/L for Gram-negative cocci (n = 12) and MIC90 of 1 mg/L for Gram-negative bacilli (n = 175). Overall the MIC90 of trovafloxacin was 1 mg/L which was equivalent to co-amoxiclav and one dilution higher than that of imipenem. The other seven comparators, including clindamycin and metronidazole, had higher MIC90 values than trovafloxacin. Trovafloxacin is likely to have clinically useful activity against anaerobes from human infection.