The susceptibility of four macrolides (erythromycin, clarithromycin, roxithromycin and azithromycin) and a ketolide (telithromycin) was tested using 58 clinically isolated strains of the 'Streptococcus milleri' group (SMG). Among the 58 strains, 9 strains were determined to be resistant to erythromycin as well as other macrolides. Of the four macrolides and the ketolide, telithromycin was the most effective antibiotic against the SMG, including the erythromycin-resistant strains.