Rhodamine dextran (RD) is widely used as both an anterograde and retrograde tracer in neurons and for numerous other applications. It is biologically rather inert having α-1,6 -linked glucose residues resistant to cleavage by most endogenous cellular glycosidases. It has low immunogenicity and makes an ideal long-term tracer for live cells. RD also serves as a valuable marker for cell loading of macromolecules by micro- injection, vesicular fusion, and electroporation, as well as for the uptake and internal processing of exogenous materials by phagocytotic and endocytic pathways.