- Bone marrow aspiration - This procedure for obtaining a bone marrow sample is optional. Normal volunteers who agree to the procedure may undergo aspiration up to three times. The hip area is anesthetized and a small sample of bone marrow is drawn through a special needle inserted in the hipbone. The first aspiration is done on a day before the G-CSF injections are started; the second is done soon after the last injection (day 6 or 7), and the third is done from 7 to 10 days after the last injection.