Three milk-resembling powders having different oil-phases were prepared and stored for six months at room temperature. Samples were taken monthly for estimation of the surface composition by "electron spectroscopy for chemical analysisz (ESCA) and analyses of the level of cholesterol oxides by gas chromatography. The highest fat coverage was obtained with technical tristearin as oil-phase. This preparation had, directly after spray-drying and during the first period of storage, around 75 % of the powder surface covered by fat. During the later storage period this coverage decreased. This powder also had the largest increase in cholesterol oxides during storage, ending in 159 µg / g cholesterol. The powder contsining highmelting pure tristearin had a low surface coverage of fat, originally about 25 % and decreased during the storage period. Little increase in cholesterol oxides was observed ending, in 52 µg / g cholesterol. The third powder containing liquid triolein as oil-phase, had a surface coverage of about 50 % throughout the storage period. The cholesterol oxidation rate was in between the two tristearin powders, ending in 75 µg / g cholesterol. The lipid present at the powder surface will undoubtedly be exposed to oxygen in air. However, lipids present inside the powder particles may also be reached by oxygen through cracks and pores in the particles. The results for the investigated powders indicate that the surface composition is of major importance for the oxidation of cholesterol. No correlation between cholesterol oxidation and solvent extractable fat (free fat) was found for the investigated powders.