- G-CSF administration All participants will have daily injections of granulocyte-colony stimulating factor (G-CSF). This drug is a genetically engineered hormone that stimulates the bone marrow to release white blood cells and white cell precursors into the bloodstream. The injections are given under the skin in the arm or leg, using a very small needle. Patients will have injections for 6 or 7 days, normal volunteers for 5. A small blood sample will be drawn each day of the injections to monitor white cell counts and changes in the number of blood cell precursors. (Smaller children and all children under 10 years of age may have blood drawn on alternate days or less to reduce the number of needle sticks and the amount of blood taken.). Larger blood draws will be taken on days 6 and/or 7 for patients and on days 5 and/or 6 for normal volunteers.