Serum levels of cytokines and in vitro cytokine production by lymph node mononuclear cells (LNMC) were studied in four patients with angio-immunoblastic lymphadenopathy with dysproteinemia (AILD) or AILD-type T cell lymphoma. An increased level of serum interleukin-6 (IL-6) was detected on initial diagnosis in both of two patients examined. Spontaneous production of IL-6 by LNMC was detected in all four patients studied. Immunosuppressive therapy with cyclosporin A (CsA) was attempted in a 68-year-old man, who was refractory to intensive combination chemotherapy. The increased level of IL-6 in this patient decreased to normal within 3 weeks of CsA administration and the patient became symptom-free. One and a half months later, the IL-6 level gradually increased along with clinical exacerbation. We also measured serum levels of IL-1 alpha, IL-2, IL-4, IFN-alpha, gamma and TNF-alpha in parallel with IL-6, but these factors were only sporadically detected. IL-6 production by LNMC was stimulated by IL-2 but inhibited by CsA. These observations suggest that IL-6 is one of the important cytokines to be involved in the pathophysiology of AILD and CsA is a useful reagent for relieving symptoms.