The excretion of individual corticosteroids in the urine of male newborn infants averaged for the first, second, and third days of life and for the sixth day of life has been studied by the method described by Birchall et al. (1963). 31 full-term, 13 premature, and 18 dysmature infants have been included, and the results compared in those pursuing a normal clinical course and in those undergoing various types of stress. The steroids have been measured individually and then summed to give the total blue tetrazolium-reducing steroids and the total sodium-fluorescent steroids. Results showed a wide range of steroid excretion by normal infants. Associated with stress, an increased steroid output was apparent in some infants of all 3 groups, indicating a response of the adrenal glands in the first few days of life. When the groups were considered as a whole, this response, measured in terms of the blue tetrazolium-reducing steroids, was statistically significant in the full-term and premature infants, but not in the dysmature infants.