The activity of the ketolide ABT-773 against 180 erythromycin-resistant Streptococcus pneumoniae obtained from children was compared with telithromycin, azithromycin, clarithromyin, roxithromycin, clindamycin, penicillin, levofloxacin and gatifloxacin. Ketolide MICs were all ≤ 1 mg/l, with ABT-773 being the most potent of all drugs tested. MIC90s for macrolides and azithromycin in mefE + isolates were 16-32 compared with > 128 mg/l for ermB + isolates. ABT-773 and telithromycin MIC90s for mefE + isolates were 0.125 and 0.5, compared with 0.032 and 0.016 mg/l for ermB + isolates and 0.5 and 1 mg/l, respectively, for isolates containing both genes. Clindamycin was active against mefE + but not ermB + isolates. 155 isolates were resistant to penicillin. All fluoroquinolone MICs were <1 mg/l. Further studies of ketolides for treatment of paediatric S. pneumoniae infections are warranted. © 2001 Published by Elsevier Science B.V. and International Society of Chemotherapy.