Cefepime, a new parenteral cephalosporin with broad antibacterial spectrum and stability to the hydrolysis to many bacterial beta-lactamases, was tested against recent blood culture isolates (369 strains of gram-negative bacilli and 131 strains of staphylococci) collected in 29 European laboratories by the microdilution method in Mueller-Hinton broth. Cefepime was very active against the gram-negative bacilli (MIC50 less than or equal to 0.016-0.064 mg/l; MIC90 0.064-4 mg/l) and less active against Pseudomonas (MIC50 4 mg/l; MIC90 greater than 16 mg/l) or Acinetobacter (MIC50 and MIC90 greater than 16 mg/l). The staphylococci were also inhibited (MIC50 8 mg/l; MIC90 16 mg/l). Cefepime was very active against bacteria producing different plasmid-encoded beta-lactamases (MIC 0.016-0.5 mg/l). Piperacillin was not active against the latter strains (MIC from 2 to greater than 64 mg/l), but the presence of the beta-lactamase inhibitor tazobactam restored the activity of piperacillin. The bactericidal activity of cefepime and piperacillin/tazobactam against beta-lactamase-producing strains was confirmed by the killing curve technique.