The immunohistochemical findings from an investigation of suppurative granulomatous lymphadenitis (SGL) are presented. With a broad panel of monoclonal and polyclonal antibodies directed against B cells, T cells, monocytes/macrophages, HLA-DR antigens, and the transferrin receptor, early, nonsuppurative granulomas were found to consist of OKM1+ OKIa1+ OKT9+ epithelioid histiocytes and multinucleated giant cells, admixed with variable numbers of OKT4+ Leu-3a+ helper/inducer T cells. These nonsuppurative lesions were surrounded by distinctive cuffs of BA1+ B1+ sIgM+ sIgD+ OKIa1+ lymphocytes. In contrast, suppurative granulomas were bordered by palisades of OKM1+ OKIa1+ OKT9+ epithelioid histiocytes, admixed with some OKT8+ suppressor/cytotoxic T cells. These suppurative lesions lacked distinctive cuffs of B lymphocytes, but half of the lesions were surrounded by numerous plasma cells that expressed cytoplasmic IgA and IgG. Based on these immunohistochemical findings, it is concluded that a shift in the nature of the predominant intragranulomatous T-cell subset occurs during the successive phases of the immune response in SGL. The cause of the central necrosis and suppuration may be related to the excessive numbers of intragranulomatous OKT8+ T cells or to the formation of immune complexes by the surrounding plasma cells.