The technicon H6000 analyzer discriminates chronic lymphocytic leukemia from other B-cell leukemias through automatic assessment of large unstained cells. The separation of chronic lymphocytic leukemia of B-cell origin from other chronic B-cell leukemias is subjective, being largely based on the morphologic features of the lymphoid cells in the peripheral blood. The percentage of large unstained cells determined with a Technicon H6000 analyzer (an automated blood cell differential analyzer, Technicon Instruments Corp, Tarrytown, NY) was used as a cell volume variable in an investigation of 70 cases of chronic lymphocytic leukemia of B-cell origin and of other chronic B-cell leukemias. The significant degree of correlation between the percentage of large unstained cells and morphoimmunophenotypic diagnosis, although obtained for a relatively small number of cases, suggests that this method of cell volume analysis can be used to improve diagnostic reproducibility in chronic B-cell leukemia. 