The advantages of a technique as a diagnostic tool for examining the distribution of bio-trace elements in the living body are discussed. Time courses of the distribution of Be, V, Mn, Fe, Co, Zn, As, Se, Rb, Sr, and Y in the upper abdomen of living selenium-deficient rats were examined using the in vivo multitracer analysis technique. The dynamics of the elements were estimated by comparison with the distribution of As. Almost all As was taken up by red blood cells. The present findings of a decrease in Se and increase in Co in the liver of Se-deficient rats are in good agreement with the previous data that showed a decrease in Se and increase in Co uptake into the liver cell fraction of Se-deficient rats. Although the normalized uptake rate and the relative distribution of Co 48h after administration increased in Se-deficient rats, the early level of the relative distribution of Co was not lower compared with that in the normal group. This suggests that the high level of the normalized uptake rate and the relative distribution of Co in Se-deficient rats were affected by the decreasing excretion rate rather than by the increasing uptake rate of Co. The plateau level of relative distribution of Se in the Se-deficient rats is lower than that in normal rats, suggesting that the lower levels of the normalized uptake rate and relative distribution of Se in Se-deficient rats were due to the decreased uptake rate of the element.