Pregnant mice were treated with a single oral dose of [carboxy-14C]2,4,5-T (100 mg/kg; 1.22 mu Ci/mg) on day 12 of gestation and sacrificed after 0.25, 0.5, 2 and 24 hours. Maternal blood, embryos, placentas and yolk sacs were analyzed by solvent extraction, TLC, and countercurrent distribution. Expressed as percentage of the administered dose/g tissue, the unchanged 2,4,5-T found in maternal blood, placentas, yolk sacs, and embryos was 3, 0.5, 0.5, and 0.2%, respectively, after 0.25 hours, and 4, 2, 2, and 0.5%, respectively, after 24 hours. No major metabolites of 2,4,5-T were detected. Urine and feces were also collected and analyzed. Radioactivity was largely eliminated in the urine, 69-78% of the administered dose in 7 days. Feces contained 5-9% of the dose. In the urine unchanged 2,4,5-T accounted for 35-44% of the dose, and 22-23% as very polar material. Unchanged 2,4,5-T in the feces was 3-5% and 1-2% as polar material. 2,4,5-T administered to pregnant mice is largely distributed and eliminated as 2,4,5-T and very polar material.