Administration of L-thyroxine into intact rats caused a distinct increase in the activity of hexokinase in liver tissue. In the isoenzyme spectrum of hexokinase the activity of hexokinase II was increased significantly. After repeated administration of insulin, liver tissue cells lost their capacity to respond to the hormone administration by induction of hexokinase. Administration of L-thyroxine into animals caused a distinct increase in the hexokinase activity in liver tissue. In isoenzyme spectrum of hexokinase under effect of L-thyroxine a significant increase in the hexokinase II activity was also observed.