The in vitro activity of cefotetan against Staphylococcus aureus and gram-negative bacterial strains including nonfermenting species has been compared with that of cefoxitin, cefotaxim, moxalactam, cefoperazone and ceftazidime by use of an agar dilution method. Cefotetan was found to be inactive against Pseudomonas aeruginosa and Acineto-bacter species and only moderately active against Staphylococcus aureus, Pseudomonas maltophilia, Pseudomonas cepacia, and Enterobacter cloacae. It was more active than cefoxitin and cefoperazone against Escherichia coli, Klebsiella pneumoniae, and indole-positive Proteus strains.