The recognition pathogenesis consequences and therapy of the deficiency state in human pregnancy are discussed. Folic deficiency is considered to be the most common water-soluble vitamin deficiency state in the U.S. especially among pregnant women. The etiology of deficiency in pregnancy involves deficient ingestion absorption and utilization defects of metabolism and the increased demands during pregnancy. The increased demand may be as much as tenfold. The minimum daily requirement seems to be 300-500 mcg throughout pregnancy. Severe anemia and megaloblastic marrow changes are late events in the deficiency state. The words and folic acid designate a group of compounds of the pteridine or pterin group. They are members of the Vitamin-B complex and are essential nutrients for humans. Leafy vegetable meats especially kidney and liver and peanuts contain measurable amounts. Cooking in large quantities of water may remove 90% of folate activity. The biochemistry of metabolism is outlined. The earliest morphologic evidence of developing deficiency is hypersegmentation of the polymorphonuclear leukocyte nucleus in peripheral blood. This phenomenon appears 8-12 weeks before megaloblastic anemia. Anticonvulsant drugs given for epilepsy may aggravate deficiency particularly if given during pregnancy. The significance of serum lactic dehydrogenase determinations in suspected cases of deficiency of pregnancy requires further study. Reports concerned with formiminoglutamic excretion are controversial regarding the value of this test in determining the deficiency state in pregnancy. Uterine cervical cytology has been found to be altered by deficiency. Remission of these changes was accomplished by therapy. Thrombocytopenia associated with megalobastic anemia of pregnancy exposes pregnant patients to an increased risk of hemorrhage during delivery. Premature separation of the placenta (abruptio placenta) and third trimester bleeding have been reported to be more frequent in cases of deficiency. However some others have not confirmed this finding. Toxemia of pregnancy with hypertension edema and proteinuria has been associated with megaloblastic anemia. Routine supplementation of diet with is recommended for all pregnant patients. A milligram of pteroylglutamate daily should suffice. The Food and Nutrition Board of the National Research Council have recommended .8 mg of supplement daily during pregnancy. The normal adult may require only 50 mcg/day.