The modification potentials of germanium on the development of preneoplastic hepatic enzyme altered foci were examined in an in vivo midterm assay system. Two week after the initial single ip dose(200 mg/kg) of diethylnitrosamine (DEN), administration of germanium at a concentration of 0.05% on the diet was commenced simultaneously with an ip injection of D-galactosamine at a dose of 300 mg/kg body wt. A11 rats were subjected to two thirds partial hepatectomy at week 5 and sacrificed for assessment of lesion yield at week 8. The modifying potential was scored by comparing the number and area per cm* of induced glutathione S-transferase placental farm-positive (GST-P) foci in the liver with those of the corresponding control group given DEN alone. Germanium showed no statistically significant increase in the number, area and mean diameter of GST-P+ foci.