Thirty low-birth-weight premature infants, between 28 and 32 weeks gestational age, were exposed to a taped recording of the mother's voice while hospitalized. These infants were matched with 30 low-birth-weight infants who did not receive supplementary auditory stimulation. Each infant's cardiac response to auditory stimuli (the mother's voice, an unknown female voice, and white noise) was measured during a testing session when an infant reached a total of 36 weeks gestational age. Measurements were recorded while the infant was quiescent and aroused. The change in heart rate to the white noise and the mother's voice teas significantly greater in the experimental group than in the control group. The results were interpreted in light of Lacey's hypothesis concerning the receptivity requirements of the situation. It was concluded that the typical environment in which premature infants are cared for while hospitalized is monotonous in terms of sensory stimulation and may be affecting the responsivity of the premature infant.