A direct influence of dietary long-chain polyunsaturated fatty acids (LC-PUFA) on the developmental quotient (DQ) of the healthy term infant remains unexplored. To test this hypothesis, we designed a prospective study of three types of diet. Twentynine infants received a LC-PUFA-supplemented formula, 31 received a standard infant formula, and 30 infants were breastfed exclusively. Neurodevelopmental response was measured by the Brunet-Lézine psychomotor development lest at 4 mo. The fatty acid status was also assessed among three diet subgroups (59 subjects) at 4 mo. Formula-fed infants who received LC-PUFA supplementation scored significantly higher (p< 0.01) on the Brunet-Lézine scale than infants who received the standard formula. Breast-fed infants also performed better than those fed the standard formula. Arachidonic acid and docosahexaenoic acid levels in circulating lipids and erythrocyte phospholipids were higher among breast-fed infants and among the group fed the arachidonic- and docosahexaenoic acid-supplemented formula. These findings are suggestive that formula supplementation with one or both of these fatty acids can benefit term infants in neurodevelopmental performance.