Decorporation therapy is the only known effective method of reducing the radiation dose to persons accidentally contaminated internally with radionuclides. Deposition of actinides in bone must be minimized because osteosarcoma appears to be the most likely pathological effect arising from systemic exposure. In previous studies, beagle dogs inhaled moderately soluble Am and Cm oxide aerosols and were then treated with diethylenetriaminepentaacetic acid (DTPA), either by repeated intravenous injection or by continuous infusion. The latter therapy was more effective in removing the actinides from the body. In this complementary study, dogs inhaled a polydisperse aerosol of 238Pu(NO3)4 and were treated as before using a single initial injection of CaDTPA (30 mumol kg-1) followed with either repeated intravenous injections of ZnDTPA (30 mumol kg-1 injection) or with subcutaneous infusion of ZnDTPA (30 or 120 mumol kg-1 day-1). Each treatment regimen commenced at 1 h after exposure and continued throughout 64 days, whereupon all animals were killed, and tissue samples and collected excreta samples were analysed radiochemically for their Pu contents. Unlike the results of previous studies with Am and Cm, in which the actinide dissolved in vivo over periods of many days to weeks, no significant differences in decorporation efficiency of 238Pu were noted for the three different DTPA-treated groups. All treatments removed about 85% of the initial pulmonary burden (IPB) of 238Pu compared with 24% IPB excreted by the saline-treated control dogs. The lack of additional effectiveness of the continuously infused DTPA was attributed to the high, initial in vivo solubility of the Pu nitrate aerosol used in this study. This resulted in a relatively rapid systemic uptake of Pu and translocation to liver, skeleton, and muscle/connective tissue, where it was less available to the longer-term action of DTPA.