Lipomelanic reticulosis of the lymph node associated with the skin diseases is well known. This work is aimed to explain the mechanism how melanin reaches the lymph node. If any solution is injected experimentally into the skin, the lymphatic capillary may be mechanically injured by the injection so that the endothelial permeability can be changed. To avoid or minimize such artifacts, melanosomes obtained from the Harding-Passey mouse melanoma by the density gradient centrifugation were injected into the abdominal cavity of mice. After fixed with the intra-aortal perfusion, the diaphragm, the mediastinal lymph nodes and blood obtained from the right atrium of the heart were investigated. Free melanosomes and phagocytized melanosomes in macrophages, features of which were identical with those of the melanosome pellet, were found in the abdominal cavity, in the connective tissue of the diaphragm and in the lymphatic lumen. The melanin. laden macrophages were also seen in the open junction of the diaphragmatic mesothelium. The intracellular melanosomes were detected in the diaphragmatic mesothelium, in the lymphatic endothelium of the diaphragm and in the phago-cytotic cells of the lymph node. The blood smear failed to show any melanin-like particles. Therefore, melanosomes are considered to have reached the lymph node not through the circulating blood but via lymphatics. The main pathway to the lymphatic lumen is thought to be through phagocytosis of the endothelium, although free melanosomes could also reach lymphatic lumen via the open junction of the endothelium.