A number of studies dealing with a lipidmobilizing hormone (LM) have been reported from these experimental and clinical laboratories.1-18 This substance was discovered, in 1954, by Seifter and Baeder.1 These investigators, working with rats and dogs, demonstrated a lipemia-clearing effect with hyaluronidase, with hyaluronate, and with deoxycorticosterone. At the same time, they found that the lipemia-clearing effect of these substances could be inhibited by the administration of cortisone or by stress (cold exposure) and by nephrosis. Studies in connection with the latter findings led to the discovery of LM in the plasma of several animal species, including man.2 Other experiments by Seifter and Baeder revealed that the pituitary was essential for the release of LM.3 More recently, LM was recovered from the posterior pituitary of hogs,4 denoting that this hormone is either produced or stored at that site. LM is dialyzable; it has been crystallized and appears to be