The pathway of asialoglycoprotein endocytosis has been elucidated in considerable detail by the use of specific pharmacological perturbants of metabolism. Biochemical assays have now been developed to monitor the dissociation of internalized receptor-ligand complex and the ensuing step of ligand-receptor segregation. Partially purified endosomic vesicles have been recovered free from contamination with lysosomes by Percoll gradient centrifugation.