Maternal folate intake and levels of folate in milk, serum and red cells were assessed in 57 healthy, lactating women, ages 22-38 years, throughout early (0-6 months) and later (7-23 months) lactation. Average maternal folate intake from diet alone was 212 µg/day or 78.5% RDA (1989) and mean total folate intake from diet and supplements was 314% RDA (878 µg/day) at 0-6 months and 238% RDA (620 µg/day) at >6 months. Human milk folate was sufficient to meet the RDA (1989) for infants. Milk folate was not related to maternal folate intake, maternal serum or red cell folate and was unaffected by extended lactation (7-23 months), perhaps at the expense of maternal folate stores. Compared with early lactation, serum folate decreased (p=0.0004) and red cell folate tended to decrease (p=0.08) in later lactation and were both increased by folate supplementation (p < 0.001).Level of folic acid supplementation appeared to predict red cell folate concentration. An average of 884 µg supplemental folate/day was associated with red cell folate levels >400 ng/mL, which have previously been reported as optimal for prevention of folateresponsive neural tube defects. The addition of an 880 µg/day folic acid supplement to the diet of lactating women may raise red cell folate concentrations of lactating women to protective levels. / Department of Family and Consumer Sciences