The cytochrome P450 CYP1A1 and CYP1B1 enzymes are phase I extrahepatic enzymes involved in the activation of pro-carcinogenic compounds to carcinogenic metabolites. Although differential overexpression of CYP1A1 and CYP1B1 has been documented at the messenger RNA (mRNA) and protein level, studies that have examined CYP1 expression by enzyme activity assays are limited. In the current study, the expression of CYP1A1 and CYP1B1 was investigated in a panel of human tumors of endometrial origin by quantitative reverse transcriptase PCR (qRT-PCR), Western blotting, and enzyme activity assays. The data revealed that approximately 36 % (5/14) and 43 % (6/14) of the endometrial tumors overexpressed CYP1A1 and CYP1B1 mRNA, whereas in 57 % of the endometrial tumors, CYP1 mRNA levels were downregulated. The mean mRNA levels of CYP1B1 and CYP1A1 in endometrial tumors did not show a significant difference compared to normal tissues (p > 0.05). Western blotting confirmed the qRT-PCR results and CYP1A1 and CYP1B1 proteins were shown to be downregulated in 7/14 (50 %) of the tumors and overexpressed in 4/14 (29 %) of the tumors. As regards to enzyme activity, 21 % (3/14) of the endometrial samples revealed elevated CYP1 activity levels across the tumor counterparts. Overall, the data suggest a putative downregulation of CYP1A1 and CYP1B1 expression in endometrial tumors, whereas overexpression of active CYP1 enzymes in 21 % of the tumors highlights the potential use of the latter enzymes as chemotherapeutic targets in endometrial cancer.