Irradiation (gamma rays, electrons or X-rays) is applied to foods for improving food safety and removing and reducing pests that are harmful to plants or plant products. As ionising radiation passes through food, it creates a trail of chemical transformations by primary and secondary radiolysis effects. The main reported radiolytic products are certain hydrocarbons and 2-alkylcyclobutanones produced from the major fatty acids in food, and some cholesterol oxides and furans. Most of these substances are also formed in food that has been subjected to other processing treatments and are thus not exclusively formed by irradiation. Furthermore, the quantities in which they occur in irradiated food are not significantly higher than those being formed in heat treatments. Since the last SCF opinion in 2003, several in vitro genotoxicity studies on irradiated foods have been published. The available data indicate that at least some 2-alkylcyclobutanones may induce DNA damage in vitro. No in vivo genotoxicity studies are available; however, a genotoxic hazard in humans is considered unlikely by the Panel in view of the plausible indirect mechanism underlying the genotoxicity of alkylcyclobutanones in vitro. Concerning other radiolytic products no new relevant toxicological studies have been reported. The weight of evidence from recent literature regarding biological effects supports the food classes and radiation doses specified in previous SCF opinion in 2003. The only new contrary evidence was indicated in publications on leukoencephalomyelopathy in cats which have been fed mainly or exclusively with highly irradiated feed. However a clear mechanistic explanation in terms of risk assessment has not been established. Considering that only a very limited quantity of food is irradiated in Europe currently, the Panel is of the view that there is not an immediate cause for concern. However, the relevance of the cats studies for human health should be clarified.