Our previous studies demonstrated that the sex-related difference in renal metabolism of N-nitrosodimethylamine in C3H/HeJ mouse was due to the sexual dichotomy of cytochrome P450 2E1 (P450 2E1) and that renal P450 2E1 in female mouse was inducible by testosterone. The present study demonstrates that the sex-related difference in renal P450 2E1 and the testosterone-mediated regulation also occurred in other mouse strains studied. The time- and dose-responses in the testosterone-mediated regulation of P450 2E1 were characterized. 19-Nortestosterone, an analog of testosterone, was shown to have an effect on the regulation of mouse renal P450 2E1 similar to that of testosterone. Testicular feminized mice (Tfm, a mouse strain devoid of functional androgen receptors) had about only one-tenth the renal P450 2E1 mRNA level as the wild-type male mice and testosterone treatment of the Tfm mice had no effect on the level of renal P450 2E1 mRNA. The result suggests that androgen receptor plays an important role in the sex- and testosterone-related regulation of mouse renal P450 2E1. To study the mechanism of the sex-related and testosterone-mediated regulation of P450 2E1 mRNA in mouse kidney, the transcription rate of the P450 2E1 gene was measured by a nuclear run-on transcription assay. Although the kidneys of male and testosterone-treated female mice had much higher steady-state levels of P450 2E1 mRNA, their transcription rates of the P450 2E1 gene were not higher than the kidneys of untreated female mice. This result suggests that the sex- and testosterone-related regulation of mouse renal P450 2E1 is predominantly at the post-transcriptional level.