Rate of degradation and half-life of ubiquinone were studied in tissues of rats, maintained on standard and artificial diet, which included either cholesterol or bile acids. Metabolism of ubiquinone was distinctly accelerated in liver, kidney tissues and skeletal muscles and was decreased in small intestine of the animals kept on the artificial cholesterol-free diet. After addition of 2% cholesterol to the ration metabolism of ubiquinone was decreased in skeletal muscles and, especially, in liver tissue. When 0.2% bile acids were included into the ration. metabolism of ubiquinone was decreased more than 13-fold in liver tissue, whereas in small intestine it was accelerated and approached the values corresponding to those of control animals.