For the post-marketing surveillance of cefmetazole (CMZ, Cefmetazon), MICs of injectable beta-lactam antibacterials including CMZ against clinical isolates from 15 medical institutions all over Japan are measured yearly and the incidence rates of resistance in various species are also evaluated. In the first surveillance from June 2000 to March 2001, 574 isolates of 13 species were tested, 548 isolates of the same 13 species were tested in the second surveillance from April 2001 to March 2002, and 654 isolates of the same 13 species were tested in the third surveillance from April 2002 to March 2003. No remarkable changes in the activity of CMZ were observed in these surveillances spanning three years. The activity of CMZ in this study was comparable to that in the studies conducted before Cefmetazon was launched. This result suggests that CMZ still maintains potent activity. Changes in percent resistance of each species to CMZ (MIC of CMZ > or = 32 microg/ml) were as follows: methicillin-susceptible Staphylococcus aureus (MSSA, 0.0% --> 0.0% --> 0.0%), methicillin-resistant Staphylococcus aureus (MRSA, 72.9% --> 87.2% --> 88.7%), Staphylococcus epidermidis (18.5% --> 31.6% --> 14.3%), coagulase-negative Staphylococcus spp. (CNS, 13.3% --> 18.2% --> 21.4%), Escherichia coli (3.6% --> 0.8% --> 2.1%), Klebsiella pneumoniae (3.4% --> 3.8% --> 2.1%), Klebsiella oxytoca (0.0% --> 0.0% --> 0.0%), Proteus mirabilis (2.3% --> 2.1% --> 0.0%), Proteus vulgaris (13.6% --> 6.7% --> 0.0%), Morganella morganii (7.3% --> 0.0% --> 14.0%), Providencia spp. (12.5% --> 0.0% --> 18.2%), Peptostreptococcus spp. (0.0% --> 0.0% --> 0.0%), Bacteroides fragilis (10.3% --> 10.8% --> 17.1%), Bacteroides spp. (78.6% --> 87.5% --> 62.5%). The Change in percent resistance of MRSA, other CNS, and B. flagiris tended to increase. It is necessary to pay much attention to trends observed in these species. Compared to other drugs tested, against MSSA, the activity of CMZ was inferior to that of CEZ, CTM, and FMOX and superior to that SBT/CPZ. Against MRSA, S. epidermidis, and CNS, the tested drugs exhibited little activity. Against Gram-negative bacteria, the activity of CMZ was almost superior to that of CEZ and CTM, and inferior to that of FMOX. Against B. flagiris and other Bacteroides spp., the activity of CMZ was almost superior to that of CEZ and CTM, and comparable to or inferior to that of SBT/CPZ and FMOX.