The accumulation and disposition of Cd2+ as CdCl2 administered orally to Japanese quail (Coturnix coturnix) was investigated. Birds received 0.01, 0.10, 1.0, 50, 500, 5000, or 50,000 micrograms Cd/kg/day for 4 consecutive days by gastric tube, and were killed 4 days after the final dose. The percentage of the total administered dose recovered in liver + kidneys + duodenum was 0.7% or less in all but the highest dose, for which recovery was approximately 2%. Only at the highest dose did the hepatic Cd concentration exceed that of the kidney, and only at this dose was there any appreciable increase in metallothionein (MT) concentrations in the liver and kidney. Duodenal cytosol was found to contain high levels (300-1300 micrograms/g) of endogenous MT-like proteins, probably due to the relatively high Zn concentration (approximately 185 ppm) of the commercial diet eaten by the quail. In the small intestine, Cd2+ taken up after trace doses of oral 109Cd2+ was found to be exclusively bound to these 10,000-MW, or lower MW, ligands. In the liver, MT synthesis was accompanied by increased concentrations of Cd and Zn (but not Cu) associated with the MT fractions, whereas in the kidney, all three metals were elevated in response to Cd-induced MT synthesis. A major conclusion of the present study is that, in response to environmentally relevant (less than 10 micrograms/kg/day po) doses of Cd2+, absorbed Cd is transported in blood primarily in a form which enhances deposition in the kidney. This behavior is consistent with the pharmacokinetics of Cd-MT.