Minimal inhibitory concentrations (MIC) of cefixime (CXM) were evaluated by agar dilution against 2,469 bacterial strains isolated in 10 hospitals. For Enterobacteriaceae, MIC 50 and 90% micrograms/ml were respectively: (I) naturally non beta lactamase producing species: E. coli and Shigella 0.25-0.5; Salmonella 0.06-0.25; P. mirabilis 0.008-0.032. (II) chromosomal penicillinase producing species: Klebsiella 0.06-2. (III) chromosomal cephalosporinase producing species: E. cloacae and C. freundii 1-greater than 128; S. marcescens 0.25-16; indole + Proteus 0.06-4; P. stuartii 0.032-0.5. Activity of CXM was not modified against plasmid-mediated penicillinase producing strains, but CXM was inactive on cephalosporinase hyperproducing strains and on broad spectrum beta lactamases producing strains. CXM was inactive on P. aeruginosa (MIC 50 and 90%: 64-128) and on A. baumannii (16-128). Haemophilus and Gonococci, regardless of beta-lactamase production status, and Meningococci were very susceptible to CXM (MIC 0.008-0.12). B. catarrhalis was generally inhibited by 0.03 to 0.5. CXM was poorly active on methicillin susceptible Staphylococci (MIC 50 and 90%: 1-64) and inactive on methicillin resistant strains. Enterococci were generally resistant whereas Streptococci and Pneumococci were inhibited by low concentrations: 0.008 to 1. These antibacterial properties place CXM in excellent position among oral cephalosporins.