The dose-dependence effects of 3 antioxidants, butylated hydroxyanisole (BHA: 2.0%, 1.0% and 0.5%), butylated hydroxytoluene (BHT: 1.0%, 0.5% and 0.25%) and ethoxyquin (EQ: 0.5%, 0.25% and 0.125%) combined with partial hepatectomy on the development of preneoplastic lesions in the liver of diethylnitrosamine (DEN, 200 mg/kg body wt)-treated rats were investigated. Feeding of the antioxidants commenced 2 weeks after the single dose of DEN used to initiate the lesions. gamma-Glutamyl transpeptidase (gamma-GT) and the placental form of glutathione S-transferase (GST-P) were used for quantitation of altered focal populations. Results with both markers demonstrated a dose-dependent decrease of foci in BHA-treated rats relative to those in control rats. Morphometric analysis of gamma-GT-positive lesions also revealed decrease in both the number and area of foci in BHT- and EQ-treated groups. The discrepancy between results of quantitation of gamma-GT- and GST-P-positive foci was attributable to the induction of a background, periportal zone staining for gamma-GT, which made differentiation of smaller foci difficult. Comparison of results with the 2 markers suggested that GST-P is the more accurate marker for quantitative studies on enzyme altered foci in rat liver.