The aim of this study was to investigate the effects of postconceptional age and voice type (male and female) on heart rate, respiratory rate, and oxygen saturation of preterm infants in the neonatal intensive care unit (NICU). Nineteen preterm infants born 31 weeks of gestation heard male and female voices on a weekly basis and their physiologic responses were recorded while hearing each voices. Results revealed that infants responded to the male voice with decreased HR as they grew older. Male voices, including the father's voice, can be considered an auditory stimulus for young preterm infants in the NICU.