1. The antihypercholesterolaemic drug ethyl α-p-chlorophenoxyisobutyrate when fed to the rat orally or mixed with the diet increased the content of mitochondria in the liver by 50–100%. Other subcellular fractions did not show any significant change. 2. In oxidative activity, respiratory control and phosphorylating ability no significant difference was observed between the mitochondria isolated from the livers of the drug-treated rats and those from normal animals. 3. In agreement with earlier reports, administration of the drug depressed the concentration of serum cholesterol and increased liver weight and the liver content of ubiquinone. However, the increase of ubiquinone was greater in the nuclear than in the mitochondrial protein.
