Absorption of U, Np, Am and Cm was increased by factors of 3.4, 7.1, 2.7 and 1.7, respectively, when nitrate solutions of these actinides were gavaged to adult rats fed an iron-deficient diet. Retention increased proportionately in liver, kidney and carcass. The concentration of the actinides excreted also increased substantially (over that of controls) in the urine of iron-deficient rats gavaged with 233U and 237Np, but not in those with 241Am or 244Cm. Weanling rats on an iron-deficient diet, gavaged with ferric nitrate immediately before administration of 238Pu nitrate, retained between 4% and 12% of the 238Pu retained by litter mates that were not treated intragastrically with iron.