The study is concerned with the presence of an unusual Lymphocyte-rich type of Hassall body in the normal human thymus. Lymphocyte-rich Hassall bodies are large, they are usually lined by squamous epithelial cells, and contain closely packed lymphocytes in areas with necrotic and hyaline material. Lymphocyte-rich areas of the HassaLL bodies do not contain epithelial cells (as demonstrated with cytokeratin 8/18, 7, 34betaE12, and MNF116), they were negative for CD20 and S100 protein. Immunoreaction for CD3 was positive in 3 of 4 cases. Our results suggest that this type of Hassall body may be involved in the negative selection of thymocytes.