Mixed-cell hepatocellular adenocarcinomas, induced by aflatoxin B1 (AFB1) in weanling rats, were allowed to develop for 18 months; age- and sex-matched controls were maintained. After 18 months, treated and control rats were administered iron dextran (ID), intraperitoneally (i.p.) as Nonemic. No gross or microscopic lesions were observed in control animals, while hepatic tumors were observed grossly in all AFB1-treated rats. Areas of apparently normal tissue, in histologic sections from control animals and in non-tumor sites of sections from AFB1-treated animals, were deeply stained for iron, both in endothelial cells and in hepatocytes, as visualized by Perls iron stain. Varying degrees of exclusion of stainable iron material were noted in histologic sections of lesions from AFB1-treated rats, as were alterations in endothelial cell staining characteristics. Iron staining clearly demonstrates the presence of varying cell populations within the induced mixed cell hepatocellular adenocarcinoma.