Twelve lymph node specimens with necrotizing lymphadenitis and which had florid necrotic lesions were studied immunohistochemically. The majority of viable lymphoid cells in the necrotic foci were CD8+ lymphocytes and KP1+ or PGM1+ phagocytizing macrophages. The CD8+ T cells were Leu1+, Leu2+, Leu3-, Leu4+, Leu5b+, Leu7-, Leu11b- and Leu19-, indicating a suppressor/cytotoxic T cell phenotype. In addition, the cytoplasm of these cells was immunoreactive for perforin and granzyme B in a granular pattern. With a nick end-labeling technique, fragmented nuclei and some lymphoid cell nuclei were positively stained. These results suggest that the necrosis in necrotizing lymphadenitis is apoptotic necrosis of T cells targeted by CD8+, perforin and granzyme-producing, activated cytotoxic T cells, supporting a viral infection etiology.