The role of steroid therapy in brain oedema following acute cerebral lesions is still unsolved. This study was conducted to compare the efficacy of dexamethasone and triamcinolone, and to analyze the influence of timing and duration of treatment on cold-induced brain swelling. In rabbits, a cryogenic lesion of the left parietal cortex was induced. 24, or 48 hrs after trauma, hemispheric swelling, water- and electrolyte-contents were measured. A first series of animals received dexamethasone, triamcinolone or saline for 24 hrs, starting treatment 10 min after trauma. In a second series, steroid treatment lasted 48 hrs and in a third series the animals were additionally pretreated for 24 hrs. Dexamethasone and triamcinolone slightly decreased posttraumatic hemispheric swelling, from 7.7% in controls to 7.0% in treated animals. There was no significant difference between dexamethasone and triamcinolone. Reduction of swelling was most pronounced in animals with 48 hrs treatment. Pretreatment with steroids was not superior to early posttraumatic treatment. On the other hand, dexamethasone and triamcinolone significantly decreased cerebral water content in the traumatized and contralateral hemisphere, as well as in non-traumatized animals. The unspecific reduction of water content by steroids in rabbits might explain the moderate therapeutical effect on brain swelling. This effect might be beneficial, nevertheless, with respect to an improvement of the intracranial compliance.