Peripheral blood mononuclear cells were isolated from an asymptomatic carrier (HAW) of the human T-cell leukemia virus type I (HTLV-I) and a patient with HTLV-I-associated myelopathy/tropical spastic paraparesis (TAN), cultivated for 24 hours in the presence (+) or in the absence (−) of 20 nmol/L Concanamycin A, and then processed to perform the concomitant detection of Tax and propidium iodide, used to determine the percentage of mortality as described in “Materials and Methods.”