An analysis of RNA and protein synthesis has been carried out on Xenopus laevis embryos, cut into two portions, during the early stages of their development. Actinomycin D was employed to inhibit the synthesis. The action of actinomycin on synthesis is stronger during gastrulation than during neurulation. In each stage a correlation between RNA synthesis inhibition and protein synthesis inhibition has been observed. In the ventral fragments of the neurula the ratio between the two inhibitions is 1:1, in the dorsal fragments it is 2:1. Messengers which existed before the treatment with actinomycin D are likely to work in protein synthesis in the dorsal fragment. This fact may be thought to be in connection with the greater hystological differentiation of the dorsal fragments. Experiments carried out on embryos in a more advanced stage of development (st. 22) and cut into three pieces confirmed this hypothesis. We observe that inhibition of incorporation in RNA compared with the inhibition in proteins increases in the order: ventral portion, dorsal portion, head. In this last portion the incorporation in protein is increased in treated embryos. This fact seems to indicate that actinomycin D inhibits the messengers controlling protein turnover.