Certain 6-(substituted-naphthyl)hydrocarbyl-4-hydroxytetrahydropyran-2-ones are unexpectedly potent in the treatment of familial hypercholesterolemia, hyperlipemia and atherosclerosis by virtue of their ability to inhibit the enzyme, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase).