Eighty-six premature infants were tested to examine the effects of maternal breast milk on infant development. Infants were classified by breast-milk consumption during the hospitalization period (M = 57.4 days) into three groups: those receiving minimal (<25% of nutrition), intermediate (25-75%), and substantial (>75%) amounts of breast milk. Infants in the three groups were matched for birth weight, gestational age (GA), medical risk, and family demographics. At 37 weeks GA, mother-infant interaction was videotaped, maternal depression self-reported, and neurobehavioral maturation assessed by the Neonatal Behavior Assessment Seale (Brazelton, 1973). At 6 months corrected age, infants were tested with the Bayley II (Bayley, 1993). Infants receiving substantial amounts of breast milk showed better neurobehavioral profiles-in particular, motor maturity and range of state. These infants also were more alert during social interactions, and their mothers provided more affectionate touch. Higher maternal depression scores were associated with lower quantities of breast milk, longer latencies to the first breast-milk feeding, reduced maternal affectionate touch, and lower infant cognitive skills. Maternal affectionate touch moderated the relations between breast milk and cognitive development, with infants receiving a substantial amount of breast milk and frequent touch scoring the highest. In addition to its nutritional value, breast milk may be related to improved maternal mood and interactive behaviors, thereby indirectly contributing to development in premature infants.