The in vitro activity of the new carbapenem SM-7338 was tested in comparison with imipenem, ceftazidime, cefotaxime, flomoxef, cefuzonam and cefmetazole against 2850 clinical bacterial isolates. SM-7338 showed good activity against a broad spectrum of gram-positive and gram-negative bacteria. SM-7338 was very active against gram-negative bacteria, inhibiting all Enterobacteriaceae, except 25% of Serratia marcescens isolates, at a concentration of 0.78 mg/l. SM-7338 inhibited the majority of Pseudomonas spp. at concentrations of less than or equal to 3.13 mg/l, its activity being twofold higher than that of imipenem. However, the activity of SM-7338 against gram-positive cocci was about one-fourth that of imipenem. Against anaerobes, SM-7338 also had the best activity of the beta-lactams tested. The compound was inactive against methicillin-resistant staphylococci, Enterococcus faecium, Xanthomonas maltophilia and Flavobacterium spp., as were the other beta-lactams. SM-7338 was quite stable in the presence of various types of beta-lactamase, but was hydrolyzed by Xanthomonas maltophilia beta-lactamase, as was imipenem. This high degree of stability was responsible for the potent activity of SM-7388 against beta-lactamase-producing species such as Enterobacter cloacae, Citrobacter freundii and Proteus vulgaris. SM-7338 also showed bactericidal activity against clinical isolates at the MIC or at concentrations slightly above the MIC.