Our aim was to assess adrenocortical function in very low birth weight infants, specifically to evaluate the impact of gestational age and dexamethasone (DEX) therapy on serum concentrations of total and free cortisol, dehydroepiandrosterone sulfate (DHEAS), and steroid-binding globulins. Twelve moderately preterm or full-term neonates of 38 +/- 4 (mean +/- SD) wk of gestation and 36 ill preterm neonates of 26 +/- 2 (mean +/- SD) wk of gestation were studied. Twenty-three of the 36 ill preterm neonates participated in a randomized neonatal DEX trial for the treatment of early chronic lung disease and received a 1-wk treatment of DEX or placebo. Serum concentrations of cortisol, corticosteroid-binding globulin (CBG), sex hormone-binding globulin (SHBG), and DHEAS were measured, and an ACTH test was performed. Gestational age correlated with the umbilical cord concentrations of total cortisol (r = 0.702, p < 0.01), free cortisol (r = 0.489, p < 0.05), DHEAS (r = 0.608, p < 0.01), and SHBG (r = 0.831, p < 0.01), but not significantly with the concentration of CBG (r = 0.428, p = 0.076). One-week DEX therapy decreased the serum concentrations of CBG (DEX 295 nmol/L, placebo 504 nmol/L; p < 0.01), DHEAS (DEX 6.5 mumol/L, placebo 11.8 mumol/L; p < 0.05), and the basal (DEX 81 nmol/L, placebo 176 nmol/L; p < 0.01) and ACTH-stimulated cortisol levels (DEX 458 nmol/L, placebo 817 nmol/L; p < 0.05). One week after discontinuation of DEX or placebo, basal cortisol concentrations did not differ significantly, but ACTH-stimulated cortisol levels were lower in the DEX-treated than in the placebo-treated infants. DEX therapy decreased the serum CBG and DHEAS concentrations and caused a transient suppression in the adrenocortical function. Despite severe illness, the very preterm neonates had relatively low basal cortisol concentrations, suggesting their reduced ability to respond adequately to stress during intensive care.