A variety of substances of endogenous and exogenous origin, when carried to the regional lymph nodes, trigger cellular reactions. The histiocytes, cells endowed with phagocytic ability, are the main reactants against such foreign bodies. They transform into macrophages, epithelioid cells, and multinucleated giant cells in an effort to segregate, phagocytose, digest, and dissolve the foreign materials. Because these arrive through the lymph node sinuses, the foreign body lymphadenopathies generally display a histologic sinus pattern, particularly involving the subcapsular sinus. The foreign substances drained by the lymph nodes may be of endogenous origin (e.g., proteins and lipids) or exogenous origin (frequently iatrogenic, a result of specific treatment modalities). The more common foreign body lymphadenopathies are further described.