High doses of dexamethasone (Fortecortin) for the prophylaxis of cerebral oedema were administered to 19 children aged 3 to 14 years because of head injury of varying degrees of severity. In order to assess possible suppression of the hypothalamic-pituitary-adrenocortical activity an insulin tolerance test and an intravenous tetracosactid (Synacthen) test was performed 1 to 26 weeks after the last dexamethasone dose. There was no evidence from the insulin tolerance test of inadequate cortisol excretion. After intravenous Synacthen injection satisfactory serum cortisol increase was found. However, from this test there was evidence of a lesser increase of serum cortisol depending on the time elapsed since cessation of dexamethasone. Investigation of circadian cortisol values showed 7 cases with subnormal serum cortisol at 18 o'clock independent of the time elapsed. The hypothalamic-pituitary-adrenocortical axis was functioning again during induced stress 7 days after withdrawal of dexamethasone. Subsequent stress situations do not require treatment with corticoids.