We evaluated adrenocortical steroid concentrations at birth and during postnatal adaptation (2 h until 7 days) in 10 vaginally delivered term small-for-gestational-age (SGA) infants and 12 term appropriate-for-gestational age infants. Plasma aldosterone, 11-deoxycorticosterone, corticosterone, progesterone, 17-hydroxyprogesterone, 11-deoxycortisol, cortisol, and cortisone were longitudinally measured by specific RIA after Sephadex LH-20 chromatography. Mean aldosterone was significantly higher in SGA than in appropriate-for-gestational-age infants (2 h to 7 days; p less than 0.001). In SGA infants, cortisone and cortisol levels were significantly lower in umbilical artery (p less than 0.05), and all glucocorticoid levels were significantly lower 12 h after birth (p less than 0.05). Thereafter (24 h to 7 days), only 11-deoxycortisol levels remained significantly lower in SGA; corticosterone and cortisol levels were even higher (p less than 0.05) in SGA 24 h after birth. The data suggest that SGA infants maintain high aldosterone levels throughout the 1st wk of life. Low cortisol and cortisone levels in umbilical artery as well as low glucocorticoid levels at 2 h and/or 12 h compared to term appropriate-for-gestational-age infants may reflect either a less stressful postnatal adaptation or, more likely, a reduced adrenocortical synthesis in term SGA infants.