Two E‐rosette (spontaneous rosette with sheep red blood cells)‐forming lymphoid cell lines were established. One (HPB‐ALL) was derived from a young male Japanese patient with acute lympho‐blastic leukemia (ALL), and the other (HPB‐MLT) was from a 62‐year‐old female Japanese patient with a leukemic T‐lymphoid malignancy. Formation of E rosettes, absence of any immunoglobulin determinants, absence of EBNA (Epstein‐Barr virus associated nuclear antigen) and very limited stimulating ability in mixed lymphocyte culture, were characteristics mostly identical with those of so far established T‐cell‐derived lymphoid cell lines, MOLT, CCRF‐CEM, CCRF‐HS‐B2, RPMI‐8402 and JM. Only HPB‐MLT, however, has been derived from an aged patient with T‐lymphoid malignancy.