Hospital treatment environments have become a major concern in recent years. Noise and illumination are potential stress sources in hospitals. The purpose ofthis study was to examine the effects of hospital noise levels and ambient illumination on newborn infants (neonates). Noise levels and lighting were varied and the effect upon neonatal heart rate, respiration rate, blood pressure, and oxygen consumption were measured. These measures are sensitive tosympathetic nervous system reactivity such as that brought about by stressful environments. In addition, noise and lighting levels were measured to determine if differences existed across conditions. Psychophysiological responses to various noise and lighting levels varied within and across neonates with some changes in the expected direction. Some unexpected results of Quiet Time were noted among neonatal intensive care staff and hospital personnel.