A method is provided for differentiation of reticulocytes. In addition, the method provides for a concurrent differentiation of leukocyte subpopulations in a blood cell sample by suitable electronic and optical measurements. The method includes exposing a blood cell sample to a reagent system to lyse mature red blood cells and subsequently analyzing reticulocytes in a flow cell by optical analysis. A concurrent differentiation of reticulocytes and leukocytes can be performed using electronic and optical analysis. Th electronic and optical analysis includes light scatter and impedance measurements. This method does not require the use of nuclear stain for differentiation of reticulocytes.