Changes in the protein contents of various organs of the germinating soy bean as well as the effect of X-irradiation on the RNA content of cotyledon of it were investigated. l) The protein content of germinating organs other than cotyledon increase while that of cotyledon decreases as germination proceeds, which is indicative of the fact that the former organs are anabolic and the latter catabolic in nature with regard to their protein metabolism during germination. 2) The cotyledon RNA content of soybean decreases until the 6th day after germination initiated, and increases thereafter. When the seeds are exposed to 300γ X-irradiation, these tendencies seem to be accelerated, bat when exposed to 600γ and 900γ X-irradiation the decrement of RNA in tile early stage is prominent and the synthetic recovery in the totes period is inhibited markedly due to radiation damage rather than radiation activation.