AbstractA larval specific high‐density lipoprotein (HDL) has been isolated from Musca domestica hemolymph by a combination of density gradient and glycerol gradient ultracentrifugations. The larval lipoprotein has a density of 1.134 g/ml and is formed by at least four apoproteins with molecular weights equal to 26,000, 23,000, 21,000, and 20,000. This lipoprotein contains large amounts of hydrocarbons and phospholipids and minor amounts of diacylglycerols and cholesterol. The larval lipoprotein is completely distinct from lipophorin in regard to apoprotein composition, lipid moiety, physiological pattern, and immunological reactions. Larval lipoprotein is accumulated until the end of the feeding period. During the pupal molt this protein is utilized and is no longer detected after 2 days of pupal stadium. The results obtained imply a possible role of this protein in the puparia and/or pupal cuticle formation. Judging from the properties shown, the Musca domestica larval lipoprotein is a completely new type of insect lipoprotein.