E1040 is a new parenteral cephalosporin with a broad antibacterial spectrum and potent antipseudomonal activity. The compound was four- to eightfold more active than ceftazidime and cefsulodin against Pseudomonas aeruginosa (MIC of E1040 for 90% of strains tested [MIC90], 3.13 micrograms/ml). E1040 also showed a potent activity against other glucose-nonfermentative rods, including Acinetobacter species. The activities of E1040 against most species of the family Enterobacteriaceae were roughly comparable to the activities of ceftazidime and cefmenoxime and exceeded that of cefotiam. Against Citrobacter freundii (MIC90, 0.78 micrograms/ml), Enterobacter cloacae (MIC90, 3.13 micrograms/ml), and Enterobacter aerogenes (MIC90, 0.2 micrograms/ml), E1040 was 16- to 256-fold more active than ceftazidime and cefmenoxime. The activities of E1040 against gram-positive cocci and anaerobes were comparable to those of ceftazidime, but the compound was less active than cefmenoxime. E1040 was at least as resistant as ceftazidime and cefmenoxime to hydrolysis by various beta-lactamases and showed high affinities for penicillin-binding protein 3 of both Escherichia coli and P. aeruginosa.