Reticulocyte count in manual method has been the assay traditionally used to evaluate the status of erythropoiesis in haematological disorders with disturbances in erythropoietic activity. But it is a qualitative rather than a quantitative test due to the high variability in manual microscopic method. Automated reticulocyte counting based on flow cytometry has provided much objective and exactly measure of percentage and absolute number of reticulocytes than microscopic method. Besides these two traditional parameters automatic reticulocyte counters can detect differences in the amounts of cellular RNA present in red blood cells which reflects their maturational stages. There are three related parameters which describes the reticulocyte maturation: RMI (reticulocyte maturity index), HFR (high fluorescence reticulocytes), IRF (immature reticulocyte fraction). These parameters can be used as the earliest signs of marrow engraftment after autologous or allogeneic bone marrow transplantations. Reticulocyte cellular indices such as MCVr (mean reticulocyte volume), CHr (reticulocyte hemoglobin content), CHCMr (reticulocyte hemoglobin concentration) entered recently in few automated reticulocyte counters allows for assessment of the functional state of the erythropoiesis in the diagnosis and monitoring of the iron deficiency and rhEpo therapy. Although there is no agreement between various methods of staining and counting of the reticulocytes and lack of standardization materials for this assay automated reticulocyte counting and new reticulocyte parameters probably will improve the diagnosis and monitoring of many haematological diseases.