Nonnutritive Sucking (NNS) has long been used to soothe crying infants. Systematic observations of this effect in newborn infants have revealed that NNS reduces arousal in general. Among preterm infants NNS has been used as an effective intervention in the newborn intensive care unit. However, there has been little systematic research on the immediate behavioral effects of NNS in this population of infants. The purpose of this study was to examine the effects of NNS on behavioral state in preterm infants. The results indicated that the amount of quiet sleep was increased following NNS, but that this increase was not greater than the amount of quiet sleep observed in two hours of undisturbed rest. These results are discussed in terms of intervention strategies which are designed to increase the amount of quiet sleep among preterm infants. It is suggested that a pacifier can increase the amount of quiet sleep when longer periods of uninterrupted sleep cannot be arranged. Additional results indicated that the rhythmic organization of state was more complex following NNS than during control conditions. A basic 40- to 60-minute rhythm in state was not affected by NNS. However, spectral analysis indicated that there were other faster frequency fluctuations in state. Following NNS there were more of these fluctuations and they accounted for more variance in state. This pattern is more similar to the pattern observed in low-risk newborns. These results are discussed in terms of inducing behavior patterns in preterm infants which are more similar to behavior seen in full term infants. Finally, a model is presented which suggests that the reduced arousal seen following NNS is an adjunct to an increase in parasympathetic activity. This increase in parasympathetic activity is hypothesized to be adaptive. Through this mechanism sucking is hypothesized to have a distinct behavioral effect on energy regulation in newborn infants outside of the requirements for feeding.