The ratio of 137Cs excreted in the urine to that in the total excreta, namely, fu value, was determined for a group of 10 Japanese male adults in continuous intake of fall-out 137Cs. The ratio averaged 0.88, ranging from 0.83 to 0.92 and was very close to those reported previously. Additionally, the ratios for Ca and stable Sr were also determined and found as 0.36 and 0.15 respectively for the same subjects.