Meropenem is a parenteral carbapenem antibacterial agent with a very broad spectrum of antibacterial activity. It is the second agent of its class to become available in Brazil. The in vitro antibacterial activity of meropenem was compared with imipenem and four other antimicrobial agents in a multicenter study. This study involved 13 clinical microbiology laboratories, 10 of which came from 8 Brazilian states. A total of 2,085 clinical isolates consecutively collected between December 1995 and March 1996 were susceptibility tested using the Etest and following the NCCLS procedures. Meropenem inhibited more than 90% of isolates of Enterobacteriaceae at 0.5 µg/mL, except for Citrobacter sp. (1 µg/ml). Generally, meropenem was slightly more active than imipenem against Gram-negative organisms and its spectrum of antimicrobial activity was broader than those of all other drugs tested. Against Pseudomonas aeruginosa, meropenem (MIC50, 0.38 µg/ml) was approximately 8-fold more active than imipenem (MIC 50,3 µg/mL). Imipenem was two-to eight-fold more active than meropenem against some Gram-positive specees oxacillin, including Enterococcus faecalis (MIC 50 of 0.75 µg/mL and 2 µg/mL respectively), oxacillin-susceptible Staphylococcus aureus (MIC 50 of 0.47 &mul;g/mL and 0.094 µg/mL), oxacillin-susceptible Staphylococcus epidermidis (MIC 50 of 0.064 µg/mL and 0.5mg/mL). Against Streptococcus sp. meropenem was slightly more active than imipenem (MIC 50, 0.016 µg/mL). The results of this study may be used to guide empiric therapy in Brazil and indicates that meropenem may have an important role in the treatment of infections caused by multiresistant strains of bacteria.