Cefuzonam [CZON, sodium (-)-(6R,7R)-7-[(Z)-2-(2-amino-4-thiazolyl)-2-methoxyiminoacetamido]-3-[(1,2,3-thiadiazol-5-yl)thiomethyl]-8-oxo-5-thia-1-azabicyclo(4.2.0)oct-2-ene-2-carboxylate] is a newly developed semisynthetic cephem with a broad antibacterial spectrum. The effects of CZON on peptidoglycan cross-linking reactions were examined in Escherichia coli, Serratia marcescens and Pseudomonas aeruginosa. The cross-linking enzyme(s) from P. aeruginosa was the most susceptible to CZON, although the bacterium was resistant to CZON. CZON was active against S. marcescens in spite of its weak inhibitory activity against the enzyme(s) from the bacterium.