[en] Flow cytometry has enormous potential in many areas of experimental pathology. Details of the installation and commissioning of a flow cytometer at the Harwell Laboratory are described. Following an explanation of the principles of flow cytometry, several applications to specific problems in radiobiology are discussed. Also included are results of some preliminary studies with the Harwell flow cytometer on samples such as blood, bone marrow, macrophages and cell cultures, and a discussion of future applications. (author)