This course focuses on principles, applications and quality assurance of flow cytometry in research and clinical use in hematology and transplantation. Emphasis is placed on the biological and physical principles underlying flow cytometry, specimen processing, operation and specific application in the identification of various hematopoietic and other cells. The use of flow cytometry to screen transplant recipients, cross-match donor and potential recipient, post-transplant monitoring, identifying HLA antigens, diagnosing hemoproliferative disorders, monitoring immunosuppressive therapy and stem cell isolation is presented. Evolving applications in other disciplines such as microbiology and clinical chemistry, will also be explored.