Several known anti-cancer agents have been shown to lead to increased expression of phase 2 metabolic enzymes without affecting phase 1 enzymes. Phase 1 cytochrome P450 (CYP) enzymes are relevant in cancer studies in that they are involved in oxidative metabolism, biotransformation and detoxification, whereas phase 2 enzyme catalysis leads to clearance. In this study, we obtained semi-quantitative measurements of cytochrome P450 (phase 1) and phase 2 microsomal epoxide hydrolase (mEH) gene expression levels in response to treatment of MCF-7 breast cancer cells with water-soluble Vernonia amygdalina (V.A.) extract. V.A., a vegetable grown in Nigeria, has potential as an anti-cancer agent. The results of Western blot and RT-PCR analyses show that V.A. extract acts as a monofunctional inducer within exposure times ranging from 2-16 hr and dose ranges from 3-100 microg/ml of V.A. Exposure of cells to low doses of V.A. did not affect expression levels of CYP1A1/1A2 mRNA, but lead to induction of mEH, thus supporting the chemotherapeutic potential of VA. However, in parallel studies, CYP3A4 gene expression was also induced, suggesting potential intermediates which influence drug-drug interactions. These data are useful toward further validating V.A. extract as a potential clinically useful natural anti-cancer agent and provide some support for the concept that modulation in CYP3A4 expression in response to treatment is relevant to prognosis.