Blood progenitor cells (BPC) are increasingly used in a variety of cli
nical settings. These include autologous and allogeneic transplantatio
n after myeloablative therapy, and gene therapy. The optimal blood pro
ducts for each of these applications have not been defined. The use of
different cytotoxic drugs and cytokines, alone and in combination, re
sults in the mobilisation of different total numbers and relative prop
ortions of primitive and committed BPC. Some cytotoxics and cytokines
not only are poor at mobilising BPC, but also are myelotoxic. Here we
review the biology of BPC mobilisation and its implications for their
clinical use.