The in vitro activities of the ketolide telithromycin and eight other antibiotics were tested against 77 strains of viridans group streptococci isolated from blood samples of neutropenic patients. Thirty-one (40.3%) of the strains were resistant to penicillin G, and 27 (35.1%) were resistant to erythromycin A. Telithromycin (MIC range of < or =0.03 to 1 microg/ml) was the most active antimicrobial tested. These data suggest that telithromycin could be useful for treatment of viridans group streptococcal bacteremia in neutropenic patients with cancer.