[en] As a radioecological study of tritium concerning with the food chain, the metabolic mechanism of tritium in the plant and the animal was investigated. Ceratopteris pterioides was cultured in a glass cylinder containing 1l of tritiated water under natural light during 28 days and 3 days. The tritium concentration of the former was higher than that of the latter and the largest leaf showed the maximum concentration of tritium. The tritium activities of free water in the lead segments cultured with tritiated water during one hour and 96 hours were observed to be 55% and 75% of initial concentration. The incorporation of tritium in the dried parts of the samples increased linearly with the time of light exposure, but the tendency decreased with cultivation, under darkness. The tritium activities in free water of rice at the period of seed and ripe time were observed approximately similar level, but in dry residue, the incorporation of tritium in the rice was observed the higher concentration at the ripe season than seedseason. Rates of tritium uptake by soybean under HTO vapor atmosphere in the chamber were measured. It required 1 day through leaves to achieve 15% activity of control. The uptake of HTO under high humidity (90%) through soybean leaves required 5 hours for reaching 66% under standard irrigation and 72% under little irrigated condition activity of vapor. On the other hand, the uptake of HTO under low humidity of 69% was shown 45% and 33% in the above mentioned condition, respectively. As an animal case the incorporation, distribution and retention of tritium in various tissues of rats were investigated during about 100 days following administration of tritiated water and tritiated leucine, and the radiation dose in various tissues was calculated. (author)