The structure of the left renal hemolymph node of young adult male Swiss albino rats has been studied by optical microscopy of semithin plastic embedded sections. Afferent lymphatics were found, opening into the subcapsular sinus through valved ostia, in a large majority of nodes. Free erythrocytes were found in the afferent lymphatics and in the subcapsular sinus. In the intermediary and medullary sinuses, erythrocytes were mostly attached to sinus macrophages. The efferent lymphatics contained few erythrocytes. All the sinuses macrophages. The efferent lymphatics contained few erythrocytes. All the sinuses contained a stained precipitate of lymph protein. The node is hypoactive in its general form but does not differ essentially from typical lymph nodes, except that it receives, through its afferent lymphatics, lymph containing numerous erythrocytes.