The minimum inhibitory concentration (MIC) of cefdinir (CI-983, FK-482), cephalexin cefuroxime, cefixime and ceftazidime were determined against clinical isolates. Cefdinir was as effective as cefixime against Haemophilus and Moraxella (Branhamella) strains and both were more effective than cefuroxime. Against streptococci, cefdinir was much more effective than cefixime and had similar efficacy to cefuroxime. Against staphylococci, cefdinir had the lowest MIC50 of all of the drugs tested. The efficacy of these antibiotics was tested against Escherichia coli K12 strains harbouring 16 of the new extended-spectrum plasmid-mediated beta-lactamases, and cefdinir was more effective than ampicillin, cephalexin, cefuroxime, ceftazidime and aztreonam.