Tentative MIC and zone diameter breakpoints were determined for moxifloxacin using BSAC criteria. An MIC breakpoint of < or =1 mg/L, denoting sensitivity, is suggested for Enterobacteriaceae, staphylococci, haemophili, moraxellae, pneumococci and enterococci. For pseudomonads high and low breakpoints of 4 mg/L and 1 mg/L are suggested to allow for an intermediate category of sensitivity. A 1 microg moxifloxacin disc content is suggested for testing all of the organisms previously mentioned, except pseudomonads, for which a 5 microg disc is needed to discriminate between the intermediate and sensitive populations. Corresponding zone diameter breakpoints for a 1 microg disc are > or = 20 mm for Enterobacteriaceae and staphylococci, 18 mm for the respiratory pathogens (Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis) and 15 mm for enterococci. For Pseudomonas aeruginosa with a 5 microg disc, three bands are suggested for interpretation, that of > or = 25 mm (sensitive), 18-24 mm (intermediate) and < or = 17 mm (resistant).