The in vitro activity of cefotetan, a new cephamycin antibiotic, was tested against 296 bacterial strains, recently clinically isolated, by measuring the minimum inhibitory concentrations. Comparisons were made with other drugs (cefoxitin, cefotaxime, piperacillin, rifampicin, clindamycin, tetracycline, chloramphenicol) widely utilized for the treatment of nosocomial infections. Cefotetan showed the highest activity against all the tested strains, with a geometrical mean of MICs (MG) of 0.32 and a MIC 50 and MIC 90 of 0.12 and 8 micrograms/ml, respectively.