Our goal was to examine whether dicamba, a widely-used broad leaf herbicide, has promoting activity in two-stage hepatocarcinogenesis. Female Sprague Dawley rats were given a single dose of diethylnitrosamine and then diets containing dicamba, or phenobarbital, or both for six months. The number and volume of placental glutathione-S-transferase-positive, glucose-6-phosphatase-negative or ATPase-negative foci were quantified in the liver. Dicamba alone did not increase the number or volume of these altered hepatic foci. Dicamba did, however, show a significant effect on the number or volume of certain markers in animals also treated with phenobarbital. These data show that dicamba in combination with other promoters may have weak promoting activity in two-stage hepatocarcinogenesis in the rat.