To establish whether glucocorticoids inhibit the arginine-vasopressin (AVP) response to physical exercise, 10 healthy men underwent bicycle ergometer tests until exhaustion (exercise control test, exercise plus dexamethasone [2 or 4 mg in an intravenous bolus]). Physiological and biochemical variables were similar in all tests. Pretreatment with dexamethasone (2 or 4 mg) partially but significantly decreased the AVP response induced by physical exercise. Our results demonstrate a partial inhibition induced by glucocorticoids of AVP neurosecretion during cycle ergometer tests.