Lymph nodes are among the organs from which biopsy specimens are most commonly obtained for diagnostic purposes. Their accessibility makes them an easy target for fine needle aspiration and surgical removal. More importantly, because of the role lymph nodes play in retaining and reacting to foreign antigens, any changes therein reflect both regional and systemic disorders. The investigation of pathologic changes, previously restricted to microscopic examination, has benefited enormously from recent rapid advances in the basic sciences, in that new techniques adapted from immunology and molecular biology can be utilized.