Lipogenesis in liver of continuously irradiated rats (dose rate of 0.57 Gy per day for up to 25 or 30 days) was increased, in comparison with control animals, between 7 and 30 days. In the liver of fed rats it was approximately five times higher than animals fasted for 16 hours before sacrifice. Lipogenesis in adipose tissue was decreased on the third day of irradiation and its value was higher than in controls between 7 and 25 days. Glyceride glycerol synthesis in irradiated rats was increased compared with controls on the first, seventh and between 21 and 25 days of continuous irradiation. We suggest that the increase in lipogenesis in the liver of continuously irradiated rats is an important factor in lipid metabolism disorders caused by the continuous irradiation.