Intoxication with uranium compounds is both an occupational risk for the workers engaged in the different processes of the elaboration of nuclear fuel and a risk for the population at large in terms of contaminated water and food. The toxic effects of uranium can be reduced by the administration of a biphosphonate, ethane-1-hydroxy-1,1-biphosphonate (EHBP), subcutaneously or intraperitoneally. The aim of the present work was to examine whether orally administered EHBP reduces the lethal effect of a single orally administered toxic dose of uranyl nitrate. Nine groups of 20 male Balb-c mice were used. Five groups received 350 mg kg(-1) of uranyl nitrate orally administered by gavage, four were co-treated 20 min later with EHBP either by gavage (350, 500, or 700 mg kg(-1)) or by subcutaneous injection (50 mg kg(-1)), and one group was not treated. Four groups of animals received only EHBP in doses and routes the same as those used in the intoxicated animals. Survival was assessed for 14 d. On day 14 the surviving animals of all groups were killed. An additional group of uranium intoxicated animals was killed on day 2 after the start of the experiment. Kidneys were examined histologically. On day 3 all the animals treated with uranyl nitrate alone and 20% of the animals treated with 700 mg kg(-1) of EHBP alone were dead. Survival at day 14 of the groups of mice intoxicated with uranyl nitrate and treated with EHBP (50 mg kg(-1) orally or 50 mg kg(-1) subcutaneously) was 45.0 and 49.6%, respectively. Tubule necrosis lesions were present in kidneys of mice intoxicated with uranyl nitrate, whereas lesions were less severe in mice treated with EHBP. Oral administration of EHBP is effective for reducing the lethal effect of uranium, and it is at least as useful as subcutaneous administration for prompt therapy of oral uranium exposure, achieving a survival rate of almost 50%.