HENRY and Kon1,2 found, by the method of Ax Mitchell3,4, that the biological value of the proteins oya, bulk of dried skim milk stored at room temperature under conditions which did not exclude atmospheric moisture gradually deteriorated from 88.5 wien the powder was a year and a half old to 71-lythree years later. At the end of the storage period the powder contained 7 per cent moisture. Findlay et al.6 had already observed that for samples of full-cream milk powder stored at 37° C. and 47° C, there was a critical moisture content below which fat deteriorated first and above which severe non-fatty deterioration was the first to occur. The latter type of deterioration resulted in unpleasant gluey flavours, marked darkening of the powder, and a great decrease in the solubility of the protein. It was immediately realized that the two observations were probably closely related. A large-scale experiment was therefore planned by the three research institutes concerned, with the object of making a thorough investigation of the changes which occur during storage of skim milk powders.