1. Since limited information is available about alterations of cytochrome P450 levels in diabetic animals other than rat, expression of P450s in the liver and kidney of the streptozotocin (STZ)-induced diabetic mouse was investigated. 2. The mRNA levels of CYP2B10, 3A11, 4A10 and 4A14 in the liver were increased in the STZ-induced diabetic mouse of both sexes. The CYP2B9 mRNA level was increased in the liver of the male diabetic mouse. These alterations were observed even at 2 weeks after administration. Insulin treatment restored these changes. The findings were consistent with changes reported in rat. 3. The levels of hepatic CYP1A2 and 2E1 and renal 2E1 and 4A did not change in the diabetic mouse at any time-point examined. No changes were seen in CYP2A- or 2C-related proteins in the diabetic mouse. These findings were in contrast to those in rat. 4. The results indicate that mouse P450s respond to insulin-dependent diabetes mellitus differently from those of the rat, and suggest that the expression of P450s in diabetes is not generally the same across animal species.