Vitamin E has been described in the literature as a regulator of gene expression. The gene-regulatory activity of vitamin E with regard to genes encoding cytochrome P450 (CYP) enzymes, which play a pivotal role both in the metabolism of xenobiotics and vitamin E, has not been conclusively characterised. The objective of the current study was, therefore, to elucidate the short- and long-term effects of natural and synthetic vitamin E on CYP gene expression using Affymetrix GeneChip® technology. To this end, HepG2 cells were incubated with 0, 10, 30, 80 and 300 μM RRR-α-tocopheryl acetate (natural vitamin E) or all rac-α-tocopheryl acetate (synthetic vitamin E) for 7 days and the mRNA of CYP genes was quantified. The expression of only one (CYP20A1) of 14 CYP genes with detectable mRNA levels was dose-dependently up-regulated. No differences in gene-regulatory activity were observed between RRR- and all rac-α-tocopheryl acetate. To study the role of vitamin E in CYP gene expression in vivo, Fisher 344 rats were randomly assigned to either a vitamin E-enriched (60 mg/kg RRR-α-tocopheryl acetate) or - deficient (1.7 mg/kg RRR-α-tocopheryl acetate) diet for 290 days. Neither in the vitamin E-enriched, nor in the vitamin E-deficient rats, were significant changes in the liver CYP, mRNA levels observed. In conclusion, our data indicated that vitamin E does not appear to modulate cytochrome P450 mRNA expression in HepG2 cells or in rats.