While the limits and variations in the fat and protein content of human milk are well established, considerable uncertainty still exists regarding the question of the amount of lactose in this fluid,1 a state of affairs largely due to the fact that while reliable and relatively simple methods for the determination of fat and protein have been in use for many years, the question of the technic of sugar determinations in milk is still unsettled. On account of the relatively large quantities of material required when lactose in milk is to be determined either by the polariscope or by one of the copper reduction methods, it is a more or less general custom, when the amount of material is limited, to calculate lactose by difference after having first determined the total solids, ash, protein and fat, a procedure which throws all the errors of the analysis on the sugar.