This study was performed to evaluate the influence of stress on growth hormone, glycerol and glucose levels in the blood in different age groups of full-term, newborn infants. Growth hormone decreased whereas glycerol and blood glucose increased after a series of heel-pricks. Since glycerol und glucose changes may well be explained by catecholamine release, the failure of the newborn infant to increase growth hormone concentration as do individuals during later life is evidence that adaptation of metabolic and hormonal reactions occurs during the postnatal period. 1 Supported by the Deutsche Forschungsgemeinschaft, Grant No. Stu 61/1.