Studies on physiology and pathology as they relate to the immune system draw heavily upon rodent models. With the increasing impetus provided by initiatives in translational medicine, the demand for ever more sophisticated, 'humanized' murine models is greater than ever. However, the design and implementation of studies in such mice is far from trivial. Here we provide a technical perspective on the increasing interest in developing humanized mice. We give examples of primary data starting with the routine procurement of human donor material, through CD34(+) cell purification prior to engraftment to injection into immunocompromised mice. Our goal is to provide practical advice to the many investigators who may be commencing or considering such studies.