The effects of acute hypoxia (2 days at 4350 m) on whole saliva flow and composition were studied on 12 sea-level natives, at rest and following a maximal exercise. Exercise, performed in normoxia and hypoxia, did not induce variations in saliva flow rate, saliva potassium or alpha-amylase concentrations. In contrast, acute hypoxia did lead to an increase in mean saliva flow rate both at rest (0.63 ml.min-1 to 0.93 ml.min-1, P less than 0.01) and after exercise (0.56 ml.min-1 to 1.06 ml.min-1, P less than 0.05) and a decrease in mean saliva potassium concentration at rest (20.8 mmol.l-1 to 14.7 mmol.l-1, P less than 0.01) as well as after exercise (21.7 mmol.l-1 to 16.5 mmol.l-1, P less than 0.05). This effect might be the consequence of a hypoxia-induced stimulation of the parasympathetic nervous system.