Lymphangiogenesis, the formation of new lymphatic vessels, is associated to numerous pathologies (1) and understanding the molecular and cellular basis of this complex process is essential for the development of novel therapeutic strategies. Studies on lymphangiogenesis have been hampered by difficulties in culturing lymphatic capillaries as three-dimensional (3D) structures in vitro that mimic the in vivo features of lymphatic vessels and lymphangiogenesis. The lymphatic ring assay described here phenocopies the different steps of lymphangiogenesis, including the spreading from a preexisting vessel, cell proliferation, migration and differentiation into capillaries. It consists on the adaptation of the aortic ring assay that has proved to be useful to investigate the molecular basis of angiogenesis (2-4). The lymphatic ring model is an ideal assay for testing the activity of lymphangiogenic agonists or antagonists. The absence of inflammatory cells allows a simple interpretation of results and the determination of direct effects of compounds on lymphatic endothelial cell properties. Another advantage of the lymphatic ring assay is that cell outgrowing are primary cells which have not been modified by repeated passages or immortalization. This culture model bridges the gap between in vitro and in vivo studies and allows genetic analysis by using thoracic ducts from genetically modified mice.