Tiron (sodium 4, 5-dihydroxybenzene-1,3-disulphonate) has been suggested as a possible antidote for acute uranium poisoning. In this study, the compound has been administered intraperitoneally to rats in dosages of 30, 300 or 1000 μmol kg-1 at 20, 60 and 180 min after the intratracheal instillation of uranyl nitrate. The amounts of uranium deposited in the lungs of rats were equivalent to intakes by workers of about 12 times the permitted daily limit of 2.5 mg. The average body content of uranium at 5 d after exposure were, respectively, about 100%, 78% and 65% of those in untreated animals. It is concluded that the administration of Tiron is of limited practical value for treatment of uranium exposures not greatly in excess of the permitted intake.