The distribution of iron and calcium in hepatic subcellular fractions of female rats treated with endrin (1,2,3,4,10, l0-hexachloro-6,7-epoxy-l,4,4~r,5,6,7,8,8aoctahydroendo,endo-l,4:5,8-dimethanonaphthalene) was determined. Endrin in corn oil was administered orally to rats in single doses of 3,4.5,or 6 mg/kg, and the animals were killed at 0,12,24,48, or 72 hr posttreatment. Iron and calcium were determined by atomic absorption spectroscopy. The administration of endrin increased the iron content of mitochondria and decreased the iron content of microsomes and nuclei. Significant increases occurred in the calcium content of mitochondria, microsomes, and nuclei. Thus, the results indicate that with respect to the subcellular distribution of iron and calcium, endrin produces differential effects. Vitamin E succinate administration partially prevented the endrin-induced hepatic alterations in iron and calcium homeostasis. Endrin also produced dose-and time-dependent increases in the liver and spleen weight/body weight ratios, while decreasing the thymus weight/body weight ratios. The altered distribution of calcium and iron may contribute to the broad range of effects of endrin.