In order to obtain information on the behavior of long-lived129I in the soil-plant-atmosphere system, two different experiments, transfer factors and volatilization of iodine, have been conducted by radiotracer techniques using125I. Soil-to-plant transfer factors varied very widely. Low values were found in tomato (0.0003) and rice (0.0019). The highest value for an edible part was seen in komatsuna,Brassica rapa L. (0.016), which is comparable to the IAEA recommended value of iodine for common crops (0.02). There was a tendency for older leaves to show higher concentrations than younger ones. The values for fruit, grain and beans were significantly lower than those for their leaves. Thus translocation of iodine with photosynthate from leaves into these plant organs was very small. Iodine in soil was found to be volatilized from the soil-rice plant system into the atmosphere as an organic iodine. Volatilization markedly decreased in the late cultivation period of rice plants.