Mathematical modeling of the regulation of blood cell production has reached a level of sophistication where it can be used to help to understand the cellular/molecular basis of some diseases like cyclical neutropenia. Equally, it has been used to suggest ways to treat some of these diseases by suggesting likely targets for drug intervention. And, lastly, the mathematics is now suggesting that there are ways in which we can avoid the hematological side effects of procedures like chemotherapy. In spite of these types of progress, however, we must recognize the very primitive nature of our modeling and that much remains to be done.