An 80-year-old patient has been followed for hepato- and splenomegaly, hemolytic anemia, neutropenia with lymphocytosis with large granular lymphocyte predominance in his peripheral blood, with infiltration of bone marrow, liver and probably also spleen. Determination of surface markers of proliferating lymphocytes in peripheral blood showed a mixed phenotype of T suppressor/cytotoxic and natural killer cells (SIg-, E+, T3+, T8+, EAC+, Leu7-, N901+, NK9+, VIB C5 and VIB E3-, Ia-). An in vitro cytotoxic test showed the functional inactivity of the cells tested also after human leukocyte interferon stimulation. Chromosomal analysis neither of peripheral blood lymphocytes nor of bone marrow cells proved the monoclonality marker. Following long-term prednisone therapy, the improvement of anemia, later also neutropenia accompanied by the decrease of lymphocytes has been achieved. As the disease present in our patient was distinguished only in recent years and in our country has not been reported yet, the details on its clinical, morphologic, hematologic, cytogenetic and mainly immunophenotypic characteristics are given in this paper. The problems concerning classification of the disease and determination of its biological nature are discussed.