Most of the early work on the irradiation of lipids was concerned with oxidative changes induced by radiation in natural fats or certain model systems analogous to fats. The autoxidation of fatty acids occurs largely via a free radical chain mechanism involving the abstraction of hydrogen atoms at positions alpha to double bonds with subsequent attack by molecular oxygen, leading to the formation of peroxy-radicals, which in turn form hydroperoxides. This reaction is usually accompanied by shifting in the position of double bonds resulting in the formation of conjugated diene systems. The hydroperoxides decompose readily and give rise to a variety of breakdown products including aldehydes, aldehyde esters, oxoacids, hydrocarbons, alcohols, ketones, hydroxy- and keto acids, lactones, and dimeric compounds. Polymerization, isomerization, and cyclization are also among the reactions typical of lipid oxidation. For more than 25 years, attempts have been in process to assess the wholesomeness of irradiated foods via animal feeding studies.