The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates induction of many drug metabolizing enzymes including cytochrome P450s (CYP1A1, CYP1A2, CYP1B1). The AhR is over-expressed in certain types of tumours, but it is unknown whether it is also over-expressed in colorectal tumours. I attempted to determine if there are changes in AhR or AhR-regulated gene expression in adenomas from C57BL/6J-Apc Min/J mice as compared to matching tissue from C57BL/6J mice. There was a significant increase in AhR mRNA in tumours from the ileum as compared to matching normal tissue from control mice in two of the four ApcMin/+ mice used. Mice which expressed increased AhR had a corresponding increase in expression of CYP1B1 and COX-2 mRNA. However, CYP1A1 expression was significantly decreased in all ileum tumors from all four ApcMin/+ mice. This work suggests that the AhR and CYP1B1 may be important as therapeutic targets against colorectal cancer.