The accumulation and subcellular distribution of Cd2+ (1 mg/kg body wt, i.p.) in the liver of the neonatal rat is age-dependent. At 4 hr after treatment the liver Cd2+ contents in the 12-day-old, 20-day-old and adult rat are similar and greater than in the 2-day-old animal. The differences in hepatic Cd2+ concentration in the older age groups are consistent with the nonlinear weight gain of the liver in the developing animal. In the hepatic cytosol Cd2+ is incorporated into a high molecular weight and metallothionein fractions and transferred from the former to the latter. This process occurs less rapidly with increasing age. The uptake of Cd2+ by the whole liver and th hepatic metallothionein is not related to the total liver concentration of Zn2+ or copper and is not significantly influenced by the concentration of pre-existing metallothionein or the concentration of thionein-bound Zn2+ or copper. The results are discussed in relation to the possible effects of Cd2+ on the liver metabolism and tissue distribution of Zn2+ and copper in the developing animal.