Using a broth microtiter dilution method, minimum inhibitory (MIC) and minimum bactericidal concentrations (MBC) were determined for the aminothiazolyl cephalosporins cefpirome and cefotaxime against 436 blood culture isolates. At concentrations of ≤16 mg/l, cefpirome inhibited 82.3% of the isolates and cefotaxime 66.5%. At the same concentrations, cefpirome killed 60.0% of the isolates and cefotaxime 46.7%. Whereas the MIC values indicated a far better activity of cefpirome than cefotaxime against oxacillin-resistant Staphylococcus aureus, Enterococci and Pseudomonas aeruginosa, the MBC values showed a poor activity of both drugs against these strains. By comparison, cefpirome was the more active agent, covering a similar spectrum to that of cefotaxime with a slight additional activity against oxacillin-susceptible 5. aureus and Staphylococcus epidermidis.