The hypothalamic-pituitary-adrenal axis (HPA) was examined in 34 ventilated preterm infants weighing < or = 1250 g during the first week of life to evaluate the association between adrenal suppression and subsequent chronic lung disease. The second aim of the study was to detect perinatal and clinical differences between the infants with and without persistent suppression of the HPA after completion of dexamethasone treatment for chronic lung disease. To evaluate the HPA, the corticotropin-releasing hormone stimulation test was performed, and the cortisol and adrenocorticotropic hormone (ACTH) levels were measured by radioimmunoassay. No association could be found between the synthesis of cortisol and ACTH at the end of the first week of life and the development of chronic lung disease. After treatment with dexamethasone, baseline cortisol levels < 138 nmol l(-1) were found in 12 infants (46.2%), 8 of whom (30.8%) had cortisol values below 83 nmol l(-1). The perinatal data of these patients did not differ from infants without HPA suppression. However, the infants with cortisol levels < 83 nmol l(-1) after dexamethasone showed a significantly shorter need for mechanical ventilation and supplemental oxygen (p < 0.01) and a lower incidence of chronic lung disease (p < 0.05).