purpose: determination effect of classical music and lullaby on hospitalized preterm infant's sleep/awake state improvement and physiologic parameters stability. study: RCT, crossover, not blinded, convenient sampling. Inclusion criteria: 1) infant GA in birth between 27w and 6d and 37w and 0d, 2)no congenital abnormality, no heart or neurologic disease, 3) intact hearing,4)no opiate, sedative or anticonvulsive therapy. Exclusion criteria: 1) all situation causes need for oxygen therapy or respiratory support, 2) increased infant distress or hypersensivity to intervention, 3) discharge, 4) parents refuse to continue. sample size: 72. 24 infants for 6 consecutive day in 3 situations, 2days in lullaby situation, 2 days in clossical music situation and 2 days in control situation, are observed.we have 6 groups based on transposition of situations.priority of groups were determined with randomization. outcome: increase o2 saturation, decrease HR and respiration and increase queit sleep in intervention situations.