The inducible expression of the cytochrome P450 2B subfamily was investigated in male C57BL/6 (B6) and DBA/2 (D2) mice, as well as their hybrids, B6D2F1, at the mRNA level. The expression of hepatic CYP2B mRNAs in B6 was lightly induced by beta -estradiol (ES), while that by phenobarbital (PB) or 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT) was prominent. Discriminating analysis showed a novelty that ES markedly induced CYP2B9 mRNA expression, whereas PB and DDT increased CYP2B10 more than CYP2B9 expression: albeit both mRNA species responded to all three inducers. Furthermore, the specific induction by ES of CYP2B9 mRNA in B6 male mice, but not D2 male mice, suggests strain dependency in the regulatory pathway of CYP2B9 expression.