Nonfat dry milk (NOM) was evaluated to determine the effect of long term storage on its sensory quality, its solubility index and on the development of oxidative derivatives of sterols. Storage variables included the form of the milk, the atmosphere in the storage container, the type of package and the storage temperature. A trained taste panel evaluated the milk for the development of cooked, metallic, and oxidized/stale flavors, mouthfeel and overall acceptability. Gas chromatography was used to determine cholesterol content and the quantity of oxidative derivatives of cholesterol present in the samples. Although long term storage of NOM did not affect the solubility index of the milk, the sensory quality of the milk was affected. Over time storage temperature and type of package had the greatest effect on sensory quality. Milk stored for 30 months at 32 C developed an unacceptable oxidized/stale flavor and at 42 months of storage, milk stored in polybags at 21 C had also developed an oxidized/stale flavor. These results substantiate the importance of controlling storage conditions during long term storage of NOM. NOM stored for four years did not develop harmful quantities of oxidative derivatives of cholesterol. However, certain expected results did occur. NOM stored in polybags developed more oxidative derivatives than samples stored in cans. Samples stored at 32 C developed more oxidative derivatives of cholesterol than any other sample analyzed and 7S-hydroxycholesterol, the only known cytotoxic derivative of cholesterol identified, was present in the samples stored at 32 C. Fresh and control samples of NOM contained similar quantities of oxidative derivatives of cholesterol.