Among gram-negative bacteria, rate of antibiotic resistance has been increasing. As a result, carbapenem is now considered as a last resort of therapeutic regimens for gram-negative bacterial infections. The choice of antibiotics has been impeded by the spread of organisms producing metallo-β-lactamases (MBL), which can confer resistance to nearly all β-lactams. MBLs have extremely diverse structures and are carried by various organisms including human pathogens. This review will focus on the classification and current status of MBL reported in Korea. (Korean J Clin Microbiol 2009;12:103-109)