1. The larval high density lipoprotein (HDL) from the hemolymph of Manduca sexta, isolated by density gradient centrifugation, contains 61% protein, 37% lipid and 2% carbohydrate. 2. The molecular weight of HDL is 6 x 10(5), with two apoproteins of 2.85 x 10(5) and 8.1 x 10(4) daltons. 3. The large apoprotein is destroyed by trypsin treatment of the particle, while the small one is not. 4. Calculations based upon size and composition show that this particle is very different in structure from mammalian lipoproteins. It is proposed that a portion of the apoprotein occupies the central core region.