The presence of Coenzyme Q (CoQ) in food, its role in cellular bioenergetics and antioxidant protection and the key role played by dietary fatty acids on membrane structure support the interest for a wide research concerning the relationship between dietary fats, CoQ content and biochemical behaviour. Several models of peroxidative stress 'in vivo' have been extensively investigated in our laboratory, with particular regards to the influence of dietary fat upon mitochondrial CoQ levels. First studies showed that the unsaturation degree of dietary fat leads to different CoQ9 and CoQ10 mitochondrial contents. The highest levels were found using polyunsaturated fat. A significant CoQ9 decrease after adriamycin peroxidative induction was found when dietary fat was polyunsaturated; on the contrary, a light increase was found in the case of monounsaturated fat. Another example of oxidative stress is that produced by food frying. The results obtained were in some cases similar to those of the previous experimental design: in fact monounsaturated dietary fats increased CoQ mitochondrial contents, whereas the polyunsaturated ones decreased CoQ levels. Finally, the combined effect of physical exercise and dietary fats on tissue and plasma CoQ levels has been studied. CoQ levels did not change during aerobic performances when dietary fat was monounsaturated whereas light increases were detected in the case of polyunsaturated fats. On the contrary, in anaerobic conditions, CoQ levels clearly increased with monounsaturated fats and no alterations were found in the case of polyunsaturated ones.