Cytochrome P450j, an enzyme involved in nitrosamine metabolism, is expressed in hepatic, pulmonary, and renal tissues and its level is elevated in ethanol- and acetone-treated rats as well as in diabetic rats induced by either streptozotocin or alloxan. Although P450j protein is substantially elevated by all inducing regimens, only in diabetic rats is P450j mRNA increased 10-fold. Nuclear run-on transcription analysis showed that this mRNA increase is not due to transcriptional activation but is due to specific stabilization of the P450j mRNA.