Biopsy specimens of lymph nodes with the histologic characteristics of angioimmunoblastic lymphadenopathy with dysproteinemia (AILD) were obtained from 9 cases (4 cases of AILD and 5 cases of AILD-like T lymphoma [AILD-T]) and histologically analyzed by the use of a double immunoenzymatic staining technique with the combination of a monoclonal antibody against lymphocyte membrane antigen and that against human DNA polymerase alpha (pol alpha), which is detectable in the nucleus of the cells in G1, S, and G2 phases. In all 9 cases, the pol alpha + proliferating cells had a peripheral T-cell phenotype with T11 and Leu-4 antigens, whereas proliferating B cells with B1 antigen were rarely observed. As for T-cell subset antigens, the proliferating T cells had T4+ helper/inducer phenotype in 7 cases, while T8+ suppressor/killer T cells proliferated in 2 cases, although a significant number of T4+ proliferating cells were also recognized. The study on malignant lymphomas that evolved in the 2 cases showed that the T-subset antigens on major proliferating tumor cells were the same as those found in the preceding AILD lesions, suggesting that lymphoma T cells originate from the AILD lesion. The results suggested that AILD without histologic manifestations of malignancy and AILD-T may be a neoplastic disease derived from either subset of peripheral T cells.