1.A similarity was found between the lactose content of the morning and evening milk of individual animals, when the samples were taken at the regular milking periods.2.The lactose content of the milk showed considerable variation between successive hourly samples.3.Hourly variations were found in the blood sugar of milking cows.4.Simultaneously collected samples of blood and milk show little or no positive correlation as to sugar content.5.In general samples of milk collected one hour later than the blood samples show a greater tendency towards higher correlation in respect to sugar than do simultaneously collected samples.6.The difficulty of the satisfactory sampling of blood and milk for comparison studies is emphasized, and an improved sampling method suggested.