Tritium metabolism in human beings was studied in volunteers who had exposure to tritiated water accidentally, by measuring the organically bound tritium with liquid scintillation counter, in sperms and plasma proteins. 2% of the initial urinary tritium specific activity was incorporated as bound tritium in sperms. In plasma proteins, on the 20th day of exposure, tritium bound in globulin was 3 times higher than that of albumin, tritium bound in globulin was 3 times higher than that of albumin.