Levels of CYP1A1 and CYP1B1 are increased in the oral mucosa of cigarette smokers. A, oral mucosal biopsies were obtained from both never smoking (never smokers, n=9) and smoking (smoker, n=9) human volunteers. Total cellular RNA was extracted from the oral mucosal biopsy samples and reverse transcribed. The expression of CYP1A1 and CYP1B1 mRNAs was assessed by RT-PCR. No bands were observed when cDNA was omitted from the PCR reaction or when the reverse transcriptase enzyme was not included in the reverse transcriptase reaction. B, Results of the data shown in panel A expressed in arbitrary units. Means and S.D. are shown; *P <0.05, **P<0.01 vs. never smokers.