For Enterobacteriaceae, MIC 50 s and MIC 90 s of cefodizime (mg/l), respectively, were as follows, for naturally non- β -lactamase-producing species: Escherichia coli 0.12 and 0.5, Salmonella spp. and Shigella spp. 0.25 and 0.5, Proteus mirabilis 0.016 and 0.03; for chromosomal penicillinase-producing species, Klebsiella spp. 0.25 and 64, and for chromosomal cephalosporinase-producing species, Enterobacter cloacae 1 and 64, Citrobacter freundii 1 and 128, Serratia marcescens 2 and 8; indole-positive Proteus spp. 0.06 and 0.5; and Providencia stuartii 0.5 and 1. The activity of cefodizime was not modified by plasmid-mediated penicillinase-producing strains but cefodizime was inactive against cephalosporinase hyper-producing strains and against expanded broad-spectrum β -lactamase-produring strains. Cefodizime was noticeably less active against Pseudomonas aeruginosa and Acinetobacter baumannii with MICs ranging from 32 to more than 128 mg/l. Haemophilus spp. and Neisseria gonorrhoeae , regardless of β -actamase producing status, as well as N. meningitidis , were highly susceptible (MIC 90 s and MIG 90 s ≤ 0.008 mg/l). Cefodizime was moderately active against methicillin-susceptible staphylococci (MIC 50 and MIC 90 8 mg/l) but failed to inhibit methicillin-resistant strains. Entcrococci were generally resistant; Streptococcus pyogenes and Str.pneumoniae were inhibited by low concentrations (MIC 50 and MIC 90 0.12 and 0.5 mg/l). A fairly wide range of MICs was found for anaerobes, with lower values for Clostridium perfringens (MIC 50 and MIC 90 0.5 and 1 mg/l) than for Bacteroides fragilis (8- > 128 mg/l). These results show that cefodizime has similar properties to other third generation cephalosporins and suggest that cefodizime would find a role in the management of hospital infections.