We report a case of a 72-year-old man with large granular lymphocyte (LGL) leukemia. Immunophenotypical analysis of the abnormal cells showed the following results: CD 2+, CD 3+, CD 4+, CD 8-, CD 11+, CD 16-, Leu 7+. These cells had natural killer (NK) activity, responded to PHA and recombinant interleukin-2 (rIL-2), and showed neither helper nor suppressor function in B-cell differentiation. Molecular genetical analysis showed monoclonal rearrangement of T-cell receptor beta-chain gene, indicating they are of T-cell origin. These findings provide information on biological characteristics of normal CD 4+, Leu 7+ cells.