Chromosomes and surface markers in lymph node cells from 2 patients with angioimmunoblastic lymphadenopathy associated with dysproteinemia (AILD) or immunoblastic lymphadenopathy (IBL) and with IBL-like T-cell lymphoma, respectively, were examined before treatment. In the patient with AILD, a small clone with chromosome abnormality was found in lymph node cells although a surface marker study failed to demonstrate monoclonality. In this patient, the clinical and cytogenetic findings suggested a subtype of lymphoma with a mild clinical course and a benign histological appearance. In the patient with IBL-like T-cell lymphoma, a high percentage of metaphases showed chromosome abnormalities such as ring chromosomes. The clinical, immunological and cytogenetic findings suggested an aggressive type of lymphoma, even though the histologic appearance was similar to that of IBL.