[en] Male Wistar-strain rats weighting approximately 380 g were used. Each animal was given a single oral administration of 5 μCi or 15 μCi of tritiated water per g body weight. Animals were sacrificed by decapitation, and blood, brain, liver, testis, and adipose tissue quickly removed. The distribution of tritium activity in these tissues and blood were investigated for 90 days. Lipids were extracted from various tissues with chloroform-methanol mixture (2:1, v/v) and analyzed by means of thin-layer chromatography. The incorporation of tritium in tissue lipids was the highest in adipose tissue, followed by brain, testis, and liver. The biological half-lives for tritium in various tissues were as follows: 33 and 213 days in brain, 80 days in adipose tissue, 10 and 38 days in testis, and 6 and 24 days in liver. Radiation dose given to each tissue during the period of 10 days (10 - 120 days after the HTO administration) ranged from 0.1 to 3.5 rads. The activity of various lipid components in the four tissues was determined during the period of 10 - 120 days. The major portion of activity in liver and testis was found in phospholipids and triglycerides, and the activity in phospholipids of both tissues decreased with time, whereas the activity in triglycerides if testis tended to increase slightly. In adipose tissue, almost all of the activity was distributed in triglycerides. In brain, the major part of the activity was recognized in phospholipids. Distribution of tritium among various phospholipid components in liver, testis and brain was also examined at 10 and 87 days after the tritium administration. The activity in phosphatidylinositol, phosphatidylethanolamine, and cerebroside of brain was retained much more than that in phospholipid components of the other tissues. (author)