This study examined the physiologic and behavioral effects of music-reinforced nonnutritive sucking (NNS) for preterm, low birthweight (LBW) infants experiencing heelstick. Subjects were 60 infants, age 32 to 37 weeks post conceptional age in a neonatal intensive care unit. Infants were randomly assigned to one of three treatment groups: pacifier-activated lullaby (PAL), pacifier-only, and no-contact. Experimental infants were provided the Sondrex PAL System, which plays music contingent on infant sucking. Pacifier-only infants did not receive music reinforcement for sucking, and no-contact infants were not provided a pacifier or music at any point during the procedure. Stress level and behavior state were assessed continuously and heart, respiratory, and oxygen saturation rates were recorded at 15-second intervals for all infants. Most physiologic data results were inconclusive. However, analysis of behavior state and stress level revealed the following significant differences for the PAL and pacifier-only groups compared to the no-contact group, all of which were greatest between the PAL and no-contact groups: lower during-heelstick behavior state means, less time in undesirable behavior states, lower during- and post-heelstick stress level means, and smaller behavior state and stress level differences between intervals. In addition, the PAL group had a significantly lower pre-heelstick stress level mean than the no-contact group. Behavior state and stress level were also more stable across time for the PAL group than the other groups, and patterns of changes in oxygen saturation, behavior state, and stress level indicate that music-reinforced NNS may facilitate return to homeostasis.