Cefpodoxime proxetil, a new oral cephalosporin, is the prodrug ester of cefpodoxime. Minimal inhibitory concentrations (MIC) of RU 51746 (sodium salt of cefpodoxime: CPD) were evaluated by agar dilution for 1 696 bacterial strains isolated in 5 hospitals. For Enterobacteriaceae, MIC 50 and 90% were respectively (micrograms/ml): (1) naturally non bêtalactamase producing species: E. coli, Shigella and Salmonella 0.25-0.5; P. mirabilis 0.06-0.12. (II) chromosomal penicillinase producing species: Klebsiella 0.12-1. (III) chromosomal cephalosporinase producing species: E. cloacae and C. freundii 2-greater than 128; S. marcescens 2-64; indole + Proteus 0.25-64; P. stuartii 0.25-16. Activity of CPD was not modified on plasmid mediated penicillinase producing strains, but CPD was inactive on cephalosporinase hyperproducing strains, and on broad spectrum bêtalactamases producing strains. CPD was inactive on P. aeruginosa (MIC greater than or equal to 64) and on A. baumannii (16-pi 128). Haemophilus, regardless on bêtalactamase production status, were very susceptible to CPD (MIC less than or equal to 0.25) and B. catarrhalis was generally inhibited by 0.12 to 1. CPD was poorly active on methicillin susceptible Staphylococci (MIC 50 and 90%: 2-4) and inactive on methicillin resistant strains. Enterococci and Listeria monocytogenes were generally resistant; Streptococci A, B, C, G and Pneumococci were inhibited by low concentration: 0.002 to 0.25 (MIC 50 and 90%: 0.016-0.032) whereas MIC for other Streptococci were 0.004 to 32 (MIC 50 and 90%: 0.25-4). These antibacterial properties placed CPD in excellent position among oral cephalosporins.