In a series of experiments, the dosimetry of OBT in the mice supplied with THO or OBT directly or indirectly from their mothers was studied. In the offspring mice nursed by mother mice supplied with THO as drinking water, the largest contribution of OBT to the total accumulated dose was found in the brain. The percent contribution of OBT to the total dose distributed between 17 and 42% among various soft tissues. The OBT localization to cell nuclei increases the microscopic dose to cell nuclei by a factor of 3 – 6 in the case of DNA-bound tritium in comparison with the dose estimated from the tissue-averaged tritium concentration. The tritium localization is of less importance in the case of protein-bound tritium. The blood level tritium was found to be useful and convenient for OBT dosimetry in a practical case of radiation protection of humans after acute and chronic intake of tritium. A new technique was developed to isolate mouse red bone marrow from tibia. A model experiment using mice has shown that the dose to red bone marrow in the case of oral THO intake was lower than the dose estimated for the blood pool.