The human hepatoma cell line, hepG2, retains many of the xenobiotic metabolising enzymes found in normal hepatocytes, including an inducible glutathione S-transferase (GST). The isoform of GST that is induced by xenobiotics in this cell line is GSTA1-1. As a first step to determining the effect of diet on induction of GST in humans, we have examined the ability of extracts from a wide variety of fruits and vegetables to induce GST activity in hepG2 cells. Extracts from cruciferous vegetables (broccoli, Brussels sprouts, cabbage) were the most potent inducers, but this was dependent on the variety. Most of the extracts from fruits, with the exception of grapefruit, were poor inducers. Similarities and differences between the induction of GST and of quinone reductase in mouse hepa 1c1c7 cells are discussed. The results show that extracts from cruciferous vegetables are effective inducers of human GST, in agreement with previous studies on GST in animals and cell lines derived from animals.