Changes in the contents of folic acid and citrovorum factor in liver and blood were examined by the subcutaneous loading injection of pteroylglutamic acid (1 mg per 100 g body weight) to the rats fed a folic acid deficient diet and to those with the normal diet. (1) The content of folic acid in blood of the two groups showed the highest value in 30 minutes or 1 hour after folic acid loading and returned to normal after 6 hours. (2) The content of folic acid in the liver of the folic acid deficient rats showed 1/3 of the control in 30 minutes after loading. (3) The content of citrovorum factor in blood of the folic acid deficient rats after folic acid loading was lower than that of control, but in 6 hours after loading the normal value was achieved. (4) The content of citrovorum factor in liver of the folic acid deficient rats was lower than that of normal value in 30 minutes after the loading, reaching about half of the control in 1 hour, and after 3 hours it returned to normal.