Hemoglobin (Hb) concentration, serum iron level, iron binding capacity and blood folate (Lactobacillus casei) activity were determined in 310 unselected pregnant Burmese women. Hb concentration was less than 11 g/dl in 72% of the women; the serum iron level was less than 50 mug/dl in 33%; serum folate activity was less than 3ng/ml in 13%; and red cell folate activity was less than 100 ng/ml in 17% of the women. Ninety-six of the women in our study were randomly divided into four groups, treated from the 22nd to the 25th week of pregnancy until full term with either ferrous sulfate containing 60 mg elemental iron twice daily, 5 mg folic acid twice daily, a combination of both, or a placebo only. At full term, Hb concentration fell in the groups given placebo or folic acid. On the other hand, in the groups given iron alone or iron plus folic acid there was an increase in Hb of 0.4 and 0.7 g/dl, respectively (intergroup difference not statistically significant). Serum iron and blood folate levels fell in the groups not receiving the appropriate hematinic. In spite of deficient serum and red cell folate levels in 30 and 40%, respectively, of the group on iron alone, the mean Hb concentration increased at full term and none of the women had a Hb concentration lower than 10 g/dl. Blood folate levels were lower in the iron-supplemented group than in the placebo group, indicating that iron deficiency does not aggravate the folate nutritional status.