Modulations in the positive hepatocyte growth factor, transforming growth factor-alpha (TGF-alpha) and its receptor epidermal growth factor receptor (EGFR), occur in rat and human liver tumors. The purpose of this study was to determine if TGF-alpha and EGFR are altered in basophilic and acidophilic preneoplastic and neoplastic liver lesions generated in DEN-initiated mice exposed to a variety of hepatocarcinogens. Female B6C3F1 mice were initiated with N-nitrosodiethylamine (DEN) and treated with hepatocarcinogenic concentrations of unleaded gasoline vapor (2,000 ppm), methyl tertiary butyl ether vapor (7,814 ppm), phenobarbital (500 ppm, diet), or chlordane (25 ppm, diet). Hepatic foci and tumors were identified and evaluated immunohistochemically with antibodies for TGF-alpha and EGFR. In all treatment groups, basophilic hepatic foci were negative for TGF-alpha immunoreactivity (554/564, 98%). In contrast, regardless of treatment, acidophilic hepatic foci were immunoreactive for TGF-alpha (107/108, 99%). There was no significant difference in mean hepatic labeling index as measured by the incorporation of 5-bromo-2'-deoxyuridine between foci immunoreactive and nonimmunoreactive for TGF-alpha. The incidence of immunoreactivity for TGF-alpha increased in hepatocellular tumors that were predominantly of the basophilic phenotype. Of basophilic hepatocellular adenomas, 16/81 (20%) were immunoreactive for TGF-alpha, while 17/29 (59%) of hepatocellular carcinomas stained positive for TGF-alpha. A similar increased incidence of EGFR immunoreactivity was found in basophilic hepatocellular adenomas (17/67, 25%) and carcinomas (19/28, 68%) relative to basophilic foci (11/367, 3%), suggesting an autocrine mechanism for the development of mouse liver tumors. The increased incidence of TGF-alpha immunoreactivity in basophilic liver tumors suggests that TGF-alpha is a marker of tumor progression in mouse liver. Furthermore, TGF-alpha modulations were dependent on phenotype rather than treatment, indicating inherent differences in the expression of TGF-alpha in basophilic and acidophilic hepatic lesions.