Arginase activity in the brain and liver and the urine contents in the brain, liver, and blood of rats on the 1st, 3rd, 30th, and 45th days of the cold acclimation (+2--+4 degrees C), were studied. The arginase activity was also studied in the brain, liver, and kidneys of adrenalectomized rats. During the acclimation, the arginase activity decreases by 1.5--2 times in the brain and increases 202.5-fold in the liver. The urine contents in the tissues raised dur to arginase activation in the liver. The brain activity of adrenalectomized animals does not differ from the control, while decreasing in the liver and kidneys by 33% and 60% respectively. We suppose that the difference between responses of the brain and liver arginases to cold is based on their different regulation by the adrenal hormones.