One hundred twelve pregnant women at 26 ± 2 weeks of gestation and with hemoglobin levels of less than 11 g/100 ml were investigated for level of hematocrit, serum iron, iron-binding capacity, serum vitamin B12, and serum folates. They were randomly divided into eight groups receiving as follows: I, placebo; II, iron; III, vitamin B12; IV, folic acid; V, iron + vitamin B12; VI, iron + folic acid; VII, vitamin B12 + folic acid; and VIII, iron, vitamin B12, and folic acid. The treatment was given for a period of 4 weeks. The women receiving iron singly or in combination showed a significant rise in hemoglobin. Vitamin B12 and/or folic acid did not enhance the effect of iron supplementation. The response to therapy was not related to initial level of serum iron, vitamin B12, or folic acid. The study clearly demonstrates that iron deficiency is the most important factor in causation of anemia in these women