The Chinese Meropenem Surveillance Study (CMSS) programme was initiated in 2003 with the aim of monitoring the antimicrobial activity of broad-spectrum agents against nosocomial Gram-negative bacilli in China. From 2003 to 2008, a total of 3892 isolates were collected from 10 teaching hospitals. The minimum inhibitory concentrations (MICs) of 11 antimicrobial agents were determined by the agar dilution method. During the study period, a marked decrease in the susceptibility of Acinetobacter spp. to meropenem and imipenem was noticed, from 94.6% to 60.7% and from 92.5% to 62.1%, respectively. However, for Pseudomonas aeruginosa the susceptibility was relatively stable, with susceptibility rates of 86.2% to 76.0% for meropenem and 74.8% to 70.5% for imipenem. Meropenem and imipenem exhibited the highest activities against enterobacterial organisms, with ranges of MIC90 values (MIC for 90% of the organisms) from 0.064 mg/L to 0.25 mg/L and 0.25 to 4 mg/L, respectively. Except for Acinetobacter spp., the next most active agent against the majority of isolates was amikacin, with susceptibility ranging from 78.8% to 93.3%, followed by piperacillin/tazobactam (73.7% to 98.2%), cefoperazone/sulbactam (63.9% to 99.1%), cefepime (67.0% to 95.4%) and ceftazidime (54.5% to 93.3%). The percentage of isolates positive for extended-spectrum beta-lactamases among Escherichia coli, Klebsiella spp. and Proteus mirabilis ranged from 50.9% to 66.7%, 25.4% to 42.4% and 8.9% to 24.2%, respectively. These CMSS results have demonstrated increasing resistance of Acinetobacter spp. to carbapenems, resulting from the spread of highly resistant clones. Continued surveillance studies, including CMSS, as well as potent measures for controlling the spread of resistant clones are required. (C) 2009 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.