The possibility of using microarray technology for mechanistic understanding of drug toxicity has opened up a new research field in Toxicology. In an attempt to build knowledge in the field, we have designed a 1C-gene array composed of 85 known human genes with toxicological interests and 15 control genes. HepG2 cells were treated with ethanol and two anticancer drugs, mitomycin C and doxorubicin. RNA were isolated and labeled by fluorescent dyes, then hybridized to the 1C-gene array. Our results showed that a number of cytochrome P450 genes, such as CYP4F2/3, CYP3A3, CYP24, and CYP51, were consistently responsive to the toxicant treatment. However, different genes response to different toxicants. For example, CYP24 and CYP51 were up regulated by the ethanol treatment but remained unresponsive to the other two drugs. The anticancer drugs, but not ethanol differentially regulated several other genes including CYP3A3, TNFRSF6 and CHES1, implying that the two drugs might function through a similar mechanism, which differs from that of ethanol. The reproducibility of our results suggests that microarray- based expression analysis may offer a rapid and efficient means of assessing drug toxicity.