This study has examined the efficacy of ZnDTPA administered in drinking water for removing 238Pu and 241Am from the rat after their simultaneous inhalation as nitrates; the dosage used was 95 μmol kg-1d-1. The continuous administration of ZnDTPA over a 14 d interval, commencing 1 h after exposure, reduced the lung and total body contents of 238 Pu to, respectively, 11 % and 18% of those in untreated rats; the corresponding values for 241Am were 11 % and 14%. After the continuous administration of 95 μmol kg-1 from 4 d to 28 d post exposure, the lung and total body contents of 238Pu were, respectively, 5% and 16% of those in controls; the corresponding values for 241Am were 7% and 19%. Further reductions in the actinide contents of body tissues were found when treatment was extended to 52 d or 76 d. These regimens were as effective as twice weekly injections of 30 μmol kg-1 ZnDTPA commencing at 4 d. After the continuous administration of 95 μmol kg-1 d-1 for 72 d, some pathological changes to the gastrointestinal tract were observed but these were considered to be reparable. It was concluded that further work is required to evaluate the toxicity of the ligand and to establish the optimal treatment regimen.