NCCLS agar dilution was used to test activity of telithromycin compared to clarithromycin, penicillin G, ciprofloxacin, levofloxacin, sparfloxacin and moxifloxacin against 26 pneumococci with defined quinolone resistance (type II topoisomerase and efflux) mechanisms. Thirteen strains were penicillin susceptible, six intermediate and seven resistant. Clarithromycin resistance (mef and/or erm) was seen in eight strains. Ciprofloxacin MICs (mg/L) were 8-64 compared to 1-32 (levofloxacin), 0.5 . or = 32 (sparfloxacin) and 0.125-4 (moxifloxacin). Telithromycin MIC50 and MIC90 values (mg/L) were 0.016 and 0.25, with only one strain having an MIC of 2 mg/L.