Abstract. BACKGROUND: Music is considered a subset of developmental supportive care. It may act as a suitable auditory stimulant in preterm infants. Also, it may reduce stress responses in autonomic, motor and state systems. OBJECTIVE: To assess and compare the influence of lullaby and classical music on physiologic parameters. METHOD: This is a randomized clinical trial with cross-over design. A total of 25 stable preterm infants with birth weight of 1000–2500 grams were studied for six consecutive days. Each infant was exposed to three phases: lullaby music, classical music, and no music (control) for two days each. The sequence of these phases was assigned randomly to each subject. Babies were continuously monitored for heart rate, respiratory rate, and oxygen saturation and changes between phases were analyzed. RESULT: Lullaby reduced heart rate (p < 0.001) and respiratory rate (p = 0.004). These effects extended in the period after the exposure (p < .001 and p = 0.001, respectively). Classical music reduced heart rate (p = 0.018). The effects of classical music disappeared once the music stopped. Oxygen saturation did not change during intervention. CONCLUSION: Music can affect vital signs of preterm infants; this effect can possibly be related to the reduction of stress during hospitalization. The implications of these findings on clinical and developmental outcomes need further study.