improving the course and outcome of patients with acute respiratory distress syndrome presents a challenge. by understanding the immune status of a patient, physicians can consider manipulating proinflammatory systems more rationally. in this context, corticosteroids could be a therapeutic tool in the armamentarium against acute respiratory distress syndrome. corticosteroid therapy has been studied in three situations: prevention in high-risk patients, early treatment with high-dose, short-course therapy, and prolonged therapy in unresolving cases. there are differences between the corticosteroid trials of the past and recent trials: today, treatment starts 2-10 days after disease onset in patients that failed to improve; in the past, the corticosteroid doses employed were 5-140 times higher than those used now. additionally, in the past treatment consisted of administering one to four doses every 6 h (methylprednisolone, 30 mg/kg) versus prolonging treatment as long as necessary in the new trials (2 mg kg-1 day-1 every 6 h). the variable response to corticosteroid treatment could be attributed to the heterogeneous biochemical and molecular mechanisms activated in response to different initial insults. numerous factors need to be taken into account when corticosteroids are used to treat acute respiratory distress syndrome: the specificity of inhibition, the duration and degree of inhibition, and the timing of inhibition. the major continuing problem is when to administer corticosteroids and how to monitor their use. the inflammatory mechanisms are continuous and cyclic, sometimes causing deterioration or improvement of lung function. this article reviews the mechanisms of action of corticosteroids and the results of experimental and clinical studies regarding the use of corticosteroids in acute respiratory distress syndrome.