A substantially purified arabinogalactan, its degradative products and selected modifications thereof have been found to act as carriers for delivering therapeutic agent to cell receptors capable of receptor mediated endocytosis (RME). The arabinogalactan and its degrative products once derivatived are capable of forming a complex between the therapeutic agent and the polysaccharide such that the complex retains the ability to recognize and bind to the RME receptor.