A study was made to determine whether low serum copper and ceruloplasmin activity values of piglets were the result of insufficient copper or insufficient serum protein. Observations were made on naturally and artificially raised piglets. In the naturally raised piglets, serum copper and ceruloplasmin activity increased from very low values to approximately those of the adult pig in one week. Two litters of artificially raised pigs were subdivided into 3 groups, each of which was fed in one of 3 dietary sequences. Pigs fed in sequence A received a mineral water solution for the first 36 hours and thereafter received cow's milk fortified with iron and copper. Sequence B pigs received the mineral water for the first 36 hours also, and thereafter were fed cow's milk fortified with iron alone. Sequence C pigs received cow's colostrum for the first 36 hours and then cow's milk as those in sequence B. The results from the artificially raised piglets indicated: (a) that ceruloplasmin protein as measured by its activity was inducible by supplementary dietary copper; (b) that rate of synthesis of hemoglobin was increased by cow's colostrum; and (c) that one of the limiting factors with the piglet under the conditions of this experiment appeared to be source of protein in early postnatal life rather than iron and copper per se.