Dexamethasone (DEX, 0.5 mg orally at 11 PM) challenge was used for the assessment of hypothalamic-pituitary-adrenal (HPA) activity in 20 normal volunteers. Age and pre-DEX serum cortisol levels were theè evaluated as predictors of postDEX serum cortisol levels using step-wise multiple regression analysis. Both age and preDEX serum cortisol levels were significant predictors of postDEX serum cortisol levels. It is suggested that the adjustment for age and preDEX serum cortisol level could be useful for the interpretation of abnormal postDEX levels.