The uptake, distribution, and elimination of tin were determined in adult and neonatal (Postnatal Day 5) rat brain following ip administration of triethyltin bromide (TET). Groups of five adult CD rats were killed at 10 min, 1 hr, 4 hr, 24 hr, 5 days, or 10 days following acute exposure to 6.0 mg/kg TET; an additional group of adult animals was killed at 24 hr following exposure to either 3.0, 6.0, or 9.0 mg/kg (N = 5/dosage). The time course for tin distribution in 5-day-old rat pups was determined by killing pups 10 min, 30 min, 1 hr, 4 hr, 8 hr, 12 hr, 24 hr, 5 days, 10 days, or 22 days following exposure to either 3.0 or 6.0 mg/kg TET (N = 4/dosage/time). Tin analyses were performed by flameless atomic absorption spectrophotometry. The t1/2 for total tin in the adult rat brain following 6.0 mg/kg TET was determined to be 8.0 days. The maximum concentration in the adult was reached at 24 hr and corresponded to 4.6, 9.6, and 16.6 ng tin/mg protein for dosages of 3.0, 6.0, and 9.0 mg/kg, respectively. Tin was evenly distributed across all brain areas studied. For animals exposed to 6.0 mg/kg TET on Postnatal Day 5, the t1/2 for total tin in the brain was 7.3 days. A maximum concentration of 9.9 ng tin/mg protein was reached at 8 hr postexposure. The rate of elimination of tin from the brain (as measured by the elimination rate constant kel) did not differ significantly between adults and neonates. However, due to a dilution effect by the rapid brain growth of the neonate, the concentration of tin in the neonatal brain following TET administration decreased significantly faster than that in the adult.