The in vitro activity of biapenem (formerly L-627 or LJC10, 627), a new carbapenem, was compared with that of imipenem and meropenem against > 6000 clinically significant pathogens isolated in six countries worldwide. Biapenem was active against members of the family Enterobacteriaceae with a 90% minimum inhibitory concentration (MIC90) ranging from < or = 0.06 to 2 micrograms/ml. Only Serratia spp. and Providencia spp. were less susceptible (MIC90, 8 micrograms/ml). Pseudomonas aeruginosa and Xanthomonas maltophilia displayed an MIC90 of > or = 8 micrograms/ml biapenem/ml whereas Acinetobacter spp. were susceptible at < or = 1 micrograms/ml. Oxacillin-resistant staphylococci were resistant to biapenem at > 8 micrograms/ml whereas oxacillin-sensitive staphylococci were susceptible at < or = 1 micrograms/ml. Biapenem, imipenem, and meropenem displayed poor activity against Ent. faecium (MIC90, > or = 8 micrograms/ml), and only imipenem displayed slightly better activity against Ent. faecalis (MIC90, 4 micrograms/ml). The rank order of activity against groups of isolates was Enterobacteriaceae (meropenem > biapenem > or = imipenem), Ps. aeruginosa (biapenem = meropenem = imipenem), oxacillin-sensitive staphylococci (imipenem > or = biapenem = meropenem), oxacillin-resistant staphylococci (biapenem = meropenem = imipenem), and Enterococcus spp. (biapenem = meropenem = imipenem). These in vitro suggest that further developmental work on biapenem is warranted.