A combination of one or more HMG-CoA reductase inhibitors (for example pravastatin, lovastatin, simvastatin, fluvastatin, rivastatin or atorvastatin) with one or more insulin sensitizers (for example troglitazone, pioglitazone, englitazone, BRL-49653, 5-(4-{2-[1-(4-2'-pyridylphenyl)ethylideneaminooxy]ethoxy}benzyl)thiazolidi ne-2,4-dione, 5-{4-(5-methoxy-3-methylimidazo[5,4-b]pyridin-2-ylmethoxy)benzyl}thiazolid ine-2,4-dione or its hydrochloride, 5-[4-(6-methoxy-1-methylbenzimidazol-2-ylmethoxy)benzyl]thiazolidine-2,4-d ione, 5-[4-(1-methylbenzimidazol-2-ylmethoxy)benzyl]thiazolidine-2,4-dione and 5-[4-(5-hydroxy-1,4,6,7-tetramethylbenzimidazol-2-ylmethoxy)benzyl]thiazol idine-2,4-dione) exhibits a synergistic effect and is significantly better at preventing and/or treating arteriosclerosis and/or xanthoma than is either of the components of the combination alone.