Although used as a condiment and essential supplement since pre-Biblical times, chlorine as a part of the molecule salt has received little research effort by large animal nutritionists. Its low cost and the continued popularity of salt as a condiment and sodium supplement has precluded the appearance of chloride deficiencies. There is great variation in the chloride and sodium content of feedstuffs fed to lactating cows so that some formulations require no supplemental chloride or sodium. Chloride is highly available from feedstuffs, and when dietary chloride is low, the cow can reduce sharply her losses of chloride in urine, feces, skin secretions, and to some degree in milk. Clinical symptoms of chloride deficiency in the lactating cow include pica, lethargy, anorexia, lowered milk yield, constipation, and cardiovascular depression. Metabolic changes are expressed as a severe primary hypochloremia, secondary hypokalemia, and metabolic alkalosis. Requirement for chloride by the lactating cow is about .20%; a working allowance of .25% seems reasonable for cows in positive energy balance. With gradual resolution of the requirements for chloride and more data on chloride in feedstuffs, use of supplemental salt for either sodium or chloride can be reduced greatly.