Ertapenem is a novel parenteral carbapenem with a long serum half-life. Its spectrum of activity is similar to that of imipenem and meropenem against Gram-positive bacteria, Enterobacteriaceae and fastidious Gram-negative bacteria but it is less active against Pseudomonas aeruginosa and Acinetobacter spp. Several studies were performed in the United States but only one European study has shown that ertapenem has an excellent activity against anaerobes. The objectives of the present study were to test the activity of ertapenem against anaerobes isolated prospectively from the lower and upper respiratory tracts, and to compare their susceptibility with that of anaerobic isolates from other body sites. Fifty-three isolates from the respiratory tract, as well as 50 isolates from various other body sites were tested with E-tests against six antibiotics. For respiratory isolates and for isolates from other sites, MIC 90 values (mg/l) were, respectively, >32 and >32 for penicillin, 0.38 and 0.75 for amoxicillin/clavulanate, 48 and >256 for ceftriaxone, 0.12 and 0.75 for ertapenem, 12 and >256 for clindamycin and 2 and 12 for moxifloxacin. The higher susceptibility of respiratory tract isolates was mainly due to the different distribution of isolated species: only three respiratory isolates but 22 other isolates belonged to the Bacteroides fragilis group. This study confirms the excellent anti-anaerobic activity of ertapenem against anaerobic isolates from the respiratory tract.