In vitro susceptibilities to meropenem and comparators of Acinetobacter strains isolated from serious infections in 37 European hospital centers participating in the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program (1997-2000) were tested. There were 635 Acinetobacter strains collected: 490 A. baumannii; 51 A. calcoaceticus var. lwoffii; and 94 other Acinetobacter strains. Overall, meropenem and imipenem were the most effective agents tested. Resistance to the antimicrobials was: 14%, meropenem; 16%, imipenem; 39%, piperacillin-tazobactam; 41%, tobramycin; 45%, ceftazidime; and 53%, ciprofloxacin. Thus, the carbapenems have useful activity against Acinetobacter spp. and represent a viable choice for treating infections caused by these organisms.