The DHA content of breast milk of women in the United States is lower than that of many other populations. Since DHA is an essential component of the structural lipids of the developing brain, and inadequate early intake may affect subsequent neurodevelopmental status, many have recommended that lactating U.S. women be supplemented with DHA. To address this issue, we studied 41 term infants who were exclusively breast-fed for the first 4 months of life. Within 5 days of delivery, each mother was assigned randomly and blindly to receive a DHA supplement of ≈200 mg/d (n=28) or a placebo (n=13) for 4 months. Plasma phospholipid fatty acid patterns of the infants were measured at 4 months of age, and neurodevelopmental status was assessed by the same individual at one year of age. The latter included the Clinical Adaptive Test (CAT)/Clinical Linguistic and Auditory Milestone Scale (CLAMS) and the Gross Motor scale of the Revised Gesell Developmental Screening Inventory. Developmental quotients (DQ) for visual problem-solving ability (CAT DQ), language development (CLAMS DQ), overall cognition (CAT/CLAMS DQ), and gross motor function (GM DQ) were determined. Mean plasma phospholipid DHA content of infants of DHA-supplemented mothers was 43% higher at 4 months of age (5.3±1.1 mol% total fatty acids) than that of infants whose mothers received placebo (3.7±0.7 mol%). Despite this, there were no statistically significant differences at one year of age in any neurodevelopmental measure between infants whose mothers were supplemented versus those whose mothers were not (CAT DQ, 116±9.4 in infants of supplemented mothers vs. 113±13 in infants of mothers who received placebo; CLAMS DQ, 108 ±15 vs. 105±14; CAT/CLAMS DQ, 112±7 vs. 109 ±10; GM DQ, 100±12.5 vs. 103±12). These data show that DHA supplementation of breastfeeding mothers increases infant plasma phospholipid DHA but confers no obvious advantage with respect to neurodevelopmental status at one year of age.