The level of ethanol-inducible cytochrome P450 2E1 (CYP2E1) in fresh lymphocytes compared with cultured cells and its induction mechanism by fasting were studied. CYP2E1 in the homogenate and S-9 fraction of fresh lymphocytes was elevated about 5-fold by fasting, comparable to the induction observed in cultured lymphocytes. This induction was accompanied by increased level of CYP2E1 mRNA, confirmed by nested RT-PCRs, Southern blot, and DNA sequence analysis. Our data thus demonstrated that CYP2E1 in fresh lymphocytes is pretranslationally induced by fasting, in parallel to the hepatic enzyme, and that measurement of CYP2E1 in the lymphocyte homogenate can be useful to estimate the hepatic CYP2E1 level in a relatively noninvasive manner.