It has been found that three proteins are associated with both dog and human chylomicrons (a droplet of fat present in the blood or lymph after absorption from the small intestine). In both species, one of these proteins has been shown to have the same N-terminal amino acid, paper electrophoretic mobility, and fingerprint pattern as does the major protein found in the density 1.063 to 1.21 plasma lipoproteins. Another protein associated with the chylomicrons has been described which is probably identical to a protein found throughout the density spectrum of human plasma lipoproteins. It is these proteins may play a fundamental role in the transport and metabolism of exogenous triglycerides.