We have evaluated the proliferative activity and DNA content of immunophenotyped hematopoietic cells applying flow cytometry. After indirect immunofluorescence the cell membrane was permeabilized for propidium iodide staining of DNA. Compared with single parameter detection of DNA content this method has more certainty in the determination of aneuploidies in lymphatic leukemia cells. Immunophenotyped residual normal hematopoietic cells were used as an internal standard. If this method was tested for evaluation of therapeutic effects after chemotherapy greater sensitivity in detection of minimal residual disease was observed than when using microscopic evaluation or single parameter DNA analysis in cases of aneuploid lymphoblastic leukemias.