LIPOPROTEIN lipase, a hydrolytic enzyme produced by many tissues, is rate-limiting for the removal of lipoprotein triglycerides from the circulation. It also has distinct roles in many normal tissues, as well as an important role in certain metabolic diseases, including obesity. More than 40 years ago, Hahn noticed that intravenous heparin totally cleared diet-induced lipemia in dogs.¹ The addition of heparin to plasma in vitro did not reproduce this effect, suggesting that the causative agent was released into plasma by heparin in vivo. This factor, ultimately identified as a triglyceride lipase, was activated in the presence of high-density lipoproteins (HDLs) . . .