Folic acid is a coenzyme for many important biochemical reactions including synthesis of purines, pyrimidines, and nucleoproteins. The recommended daily allowance of folic acid is 65 - 200 microg/day for infants and children. The recommended dose for deficiency states is 1000 microg/day; the effects of excess amounts of folic acid are unknown. The role of folic acid in preventing progression of arteriosclerosis is rather a new issue. Thrombotic events related to slightly elevated levels of homocystein in adults may be decreased by daily consumption of 1 mg of folic acid together with 5 - 100 mg of pyridoxine.