The usefulness of the determination of the tritium concentration in blood for estimating the average soft tissue dose after tritium intake was tested. Tritiated water and a mixture of tritiated amino acids dissolved in saline solution were separately administered to adult male mice by intraperitoneal injection. The tritium levels in the blood, urine, whole body, spleen, liver, testis, and brain were then determined at various periods. With both types of tritium administration, the results suggested that the accumulated dose in the blood pool gave a conservative estimate of the accumulated dose to the soft tissue.