We investigated on the rapid and easy method for the determination of peripheral blood stem cell (PBSC) using the immature information channel (IMI) of the automated hematology analyzer (SE-9000). The IMI channel provides information regarding immature leukocytes, including blast cells and immature granulocytes. CD34 positive cells, which are detected as the CD34 antigen on hematopoietic stem cells, were purified from the fractionated peripheral blood stem cell harvesting samples using Isolex. These purified CD34 positive cells accumulated in the gate corresponding to low Recurrent Frequency values which was presented on IMI channel analysis. Thus, the software for the IMI channel analysis to detect only the cells accumulated in this gate was developed (HPC program). The peripheral blood samples were collected from the subjects (22 cases) before and after chemotherapy. Using HPC program, the regression coefficient value between the ratio of IMI positive cells and CD34 positive cells in the peripheral blood samples was 0.81 (n = 122). As SE-9000 enables to determine the number of PBSC easily and rapidly, the measurement of IMI positive cells is clinically useful for the monitoring of the rise in PBSC after chemotherapy for mobilization.