Two cows, receiving an excellent dry ration consisting of well-cured alfalfa hay, mangel beets, and a good grain mixture (Ca/P ratio 1.09–1.19), and yielding 27 and 22 kgs. of milk daily, remained in prevailingly negative calcium and phosphorus balances throughout a period of seven weeks. This occurred in the early part of the lactation period. During the last three weeks of the experiment the introduction daily of one-half hour's exercise produced slight and probably insignificant effects on the calcium and phosphorus metabolism but a very marked effect on the nitrogen metabolism. Without allowing for exercise, the animals received 5 per cent more than their energy requirements calculated on the basis of the Savage standard.