SUMMARY In a dry cow with a permanent parotid fistula, the concentration of sodium and potassium in pure parotid saliva and in mixed saliva collected with a sponge from the cheek were compared. Changes in the composition of the sponge samples reflected those in the parotid saliva during the induction of sodium deficiency. Mixed saliva samples were taken from 6 lactating cows first on a stall diet and then when grazing grass heavily fertilized with ammonium sulphate and potassium chloride. The grass evoked an aldosterone-like effect on the saliva composition, with a rise in potassium and fall in sodium concentration. The response of individual animals differed greatly in timing and intensity.