OBJECTIVE Methyl tertiary butyl ether (MTBE) is a new gasoline additive, with certain carcinogenecity in animal experiments. To study its possible mechanism of carcinogenesis in animals, expression of protooncogene c-myc and functional gene glutathione S-transferase-P (GST-P) in the liver tissues of rats chronically exposed to MTBE was detected. METHODS Forty male SD rats with body weights of 180 - 200 grams were randomly divided into four groups and gavaged with MTBE dissolved in soybean oil with doses of 1 000, 600, 200 and 0 mg/kg, respectively, once daily and five days a week for 13 weeks. Liver tissues of the animals were frozen quickly in liquid nitrogen and their total RNA extracted with one-step method. The probes of c-myc and GST-P were labeled with digoxin by random primer method, and dots hybridization with RNA was used. RESULTS Levels of expression of c-myc gene in the liver tissues of rats increased significantly, but not for those of GST-P. CONCLUSIONS MTBE can induce the higher expression of c-myc gene, which suggests it can promote cell proliferation-one of possible mechanisms of carcinogenesis in animals.