A unique T-cell line, MT-2, was established from normal human cord leukocytes of a male infant by co-culturing with leukemic T-cells from a female patient with adult T-cell leukemia. MT-2 cells expressed receptors for sheep erythrocytes and complement and were reactive with anti-T-cell and anti-Ia sera. They were negative for Fc receptors, surface immunoglobulin, and Epstein-Barr virus nuclear antigen. Chromosomally, the MT-2 line was male and most cells were shown to have a normal diploid karyotype. The cultured cells were tumorigenic when transplanted into immunosuppressed newborn hamsters.