A patient with T-cell chronic lymphocytic leukemia presented with severe megaloblastic anemia with normal serum folic acid and cobalamin concentrations. BFU-E could not be cultured from the patient's peripheral blood unless T-lymphocytes were removed by E-rosette formation. Inhibitory activity by the patient's T-cells was restricted to autologous BFU-E. After cyclic chemotherapy the anemia and megaloblastic changes resolved, peripheral blood BFU-E could be cultured from unfractionated peripheral blood and the T-cell inhibitory activity could no longer be demonstrated. The anemia in this patient is probably due to the neoplastic expansion of a suppressor T-lymphocyte population.