A previously healthy 74 year old woman presented with T-cell chronic lymphocytic leukemia, lymphadenopathy, hepatosplenomegaly and a mediastinal mass. The circulating lymphocytes were small to medium in size (some with convoluted nuclei) and W rosette-positive; they could be assigned to the inducer-helper subset of T cells with the acid of monoclonal antisera. These cells reacted with OKT3, which detects peripheral T cells; OKT4, which detects the inducer-helper subset of T cells; and OKT11, which detects the sheep cell receptor. It is noteworthy that they were also positive for the la-like antigen found on T cells only after activation. Microscopic examination of a lymph node biopsy specimen revealed a diffuse pattern of pleomorphic large cells characteristic of the T-cell lymphomas and lymphocytic leukemias reported from Japan. However, the lymph node cells lacked the T-cell differentiation antigens present on the circulating lymphocytes. The findings in this case provide insight into the pathogenesis of this unusual disorder and are relevant to our understanding of the spectrum of surface antigens in the more common malignant lymphomas.