A leukemic T-cell line, designated as TALL-1, has been established in continuous culture from the bone marrow of a patient with a leukemic phase of T-cell lymphosarcoma. TALL-1 cells have T-cell properties and lack Epstein-Barr virus or its genome. The cells of TALL-1 line are considered to have originated from the donor's leukemic cells on the basis of their cytogenetic, morphological, and surface features.