[en] A special feature of tritium radiation is the very low energy of the beta particles (5.7 keV average, 18 keV maximum). This low energy results in very short particle ranges in tissue, ranges that are less than cell dimensions. Another result of the low energy is that the ionization density along beta-ray tracks (even though the tracks are short) is significantly greater than that associated with secondary electrons from gamma rays. The studies of tritium radiotoxicity reviewed, involving chronic ³HOH exposures in mammals, demonstrate in both mice and monkeys that biological effects can be measured following remarkably low levels of exposure --- levels in the range of serious practical interest to radiation protection. (Namekawa, K.)