[en] Tritium levels in urine and blood samples of occupationally exposed persons were investigated with a Tri Carb liquid scintillation counter. The concentrations in the urine were determined as tritiated water and those in the blood as total tritium. The methods are described. The detection limit for HTO was about 2 pCi/ml and that for total tritium 7 pCi/ml. Tritium concentrations in daily urine of occupationally exposed persons at the Reactor Centre, Seibersdorf, were up to 10 pCi HTO/ml. The arithmetic mean of the results of investigations on 16 persons was 3.8+-2.1 pCi HTO/ml. Tritium levels in blood were notably higher than expected for a homogeneous distribution of HTO in the body fluids. Tritium concentrations in the blood of occupationally exposed persons at the Centre varied between 26 and 58 pCi/ml. An estimation of tritium intake based on these results showed, in the most unfavourable case, no more than 0.5% of the maximum permissible body burden for occupationally exposed persons. (author)