Recent biochemical and morphological studies using the MDCK cell line have provided insights into the organization of the endocytic pathways in an epithelial cell. The cytoskeletal organization of these cells has been described and evidence for the involvement of microtubules in facilitating endocytic traffic has been obtained. The findings with this model system are compared to results from in vivo studies of the endocytic pathways from the surface domains of specialized epithelial cells and to studies of endocytosis in neurons.