The literature evidencing the role of iron in promoting a range of neoplasms in humans and animals prompted us to search for a possible association between chemically induced hemosiderosis and hemangiosarcomas in the liver of mice in selected studies conducted by the National Toxicology Program (NTP). Its historical control database was examined for studies in which treatment-related liver hemangiosarcoma was noted; 130 consecutive NTP studies in B6C3F1 mice from Technical Report (TR)-340 to TR-493 were evaluated. Three compounds (2-butoxyethanol, p-nitroaniline, and para-chloroaniline) were associated with a relatively high incidence of Kupffer cell pigmentation consisting of hemosiderin in both sexes; only the male mice developed a relatively low incidence of treatment-related hemangiosarcoma. With a fourth compound (o-nitroanisole), a relatively low incidence (16/50, high-dose males) of chemical-related hemosiderosis was noted, with no associated increase of hemangiosarcoma. Two chemicals (pentachlorophenol and tetrafluoroethylene) increased the incidence of liver hemangiosarcoma in male and female mice, with no increase in Kupffer cell pigmentation. The overall association between liver hemangiosarcoma and Kupffer cell pigmentation was highly significant (p < 0.001). The cause for hemosiderosis in all cases was the erythrocytic hemolytic effect of the compounds. The reason for the sex-increased susceptibility for development of hemangiosarcoma is unknown but may be due to a hormone-related, reduced antioxidative defensive capacity through modulation of the activities of antioxidative enzymes.