The absorption of U within the male Wistar rat was determined following oral gavage with uranyl nitrate solutions at seven different dosages. Gavage levels ranged from 0.003 to 45 mg U per kilogram body weight. Uranium tissue burdens were determined at 0.25, 0.5, 1, 2, 4, 8, 24, 48, 96 and 240 h following gavage. Blood, kidney, liver and bone were analyzed for U content using neutron activation followed by delayed neutron counting. Uranium rapidly localized in the kidneys and bone following ingestion. Bone was found to be the primary tissue of deposition. Skeletal and kidney burdens closely paralleled each other from 15 min to 10 d after oral gavage. Uranium burdens in the blood reached a maximum within 30 min but declined rapidly thereafter. Burdens of all tissues were well correlated with each other and with dosage at all dose levels. Equations relating body burdens with blood levels were developed and found to be useful for predicting body burdens for the initial 8 h following gavage. Gastrointestinal absorption (f1) was 0.6-2.8% over the range of U administered. Movement of U through the GI tract was assessed at two dosages. The transit time of U through the GI tract was approximately 48 h. Uranium loss from the stomach was described as a power function of time. The maximum value in the small intestine was attained within 2 h, and thereafter its rapid loss was linear up to 8 h. A minor residual loss component from the small intestine was evident beyond 8 h post-gavage.