This review describes a new method of reticulocyte analysis based on flow cytometry, better than manual reticulocyte counting. Reticulocyte percentage, absolut number, indexes of maturity (RMI- Reticulocyte Maturity Index, IRF ? Immature Reticulocyte Fraction) and others qualitative parameters express the erythropoietic activity of kidneys and bone marrow. The new proposed parameters can improve the diagnosis of anemias and others haematological disorders like leukemia, myelodysplastic syndrom. They also provide exactly and early information about the status of bone marrow after ablative chemotherapy and transplantation. Automated reticulocyte counting can create new potentials for haematology diagnosis.