Pregnant Syrian hamsters were given a dose of 3.9 micromoles cadmium ion/kg (radiolabelled with 109cadmium) on days 7, 8, 9, and 11 of gestation. Animals were sacrificed on day 13 of gestation and maternal blood, liver, kidney, placentas, and fetuses collected. No pathology was observed in placentas or fetuses. Maternal liver accounted for 61% of the total cadmium injected (15.6 micromoles/kg dam), maternal kidney 4%, and placentas 0.24%. Maternal blood and fetuses contributed negligibly to the total body burden of cadmium. Gel filtration experiments indicated two major cadmium fractions in maternal liver, maternal kidney, and placental cytosols, one at the excluded volume and another nearly twice the excluded volume. Further purification and characterization of the cadmium fraction eluting at twice the excluded volume in the gel filtration experiments showed it to be cadmium metallothionein. Ion exchange chromatography on DEAE Sephacel revealed two forms of cadmium metallothionein in the cytosols of maternal liver and placentas. Maternal kidney cytosols contained one cadmium metallothionein. Amino acid analyses suggest that the thionein components of placental cytosols are synthesized in situ.