DEPs (diesel exhaust particles) like any other particles can be also inhaled into lung to participate in a damaging reaction to the organ. Possible damages might be apoptosis and inflammatory responses to the cells in respiratory track. The aim of this study was cytotoxicity evaluation of DEPs from five in-use diesel vehicles using a murine macrophage cell (RAW 254.7). We found that most DEPs have a considerable cytotoxicity compared to the control and SRM 2975. When measured by MTT assay and extents of apoptosis, DEPs of two highmileage vehicles had higher toxicity than those of the other three low-mileage vehicles tested. Although mRNA expression level of TNF-${alpha$ somewhat explains the trend of cytotoxicity and apoptosis, that of IL-1$eta$ did not. Correlation studies among the extents of MTT assay, apoptosis, and TNF-$alpha$ expression showed that the extents between apoptosis and TNF-$alpha$ expression was most highly correlated (r=0.96). These results suggest that cytotoxicity of various DEPs could be compared easily by measuring the extent of apoptosis or TNF-$alpha$ expression by DEPs.