From DONOR FAQ (http://www.samarinfo.org/donorfaq.asp http://www.samarinfo.org/donorfaq.asp) by South Asian Marrow Association of Recruiters: Marrow donation:

From DONOR FAQ (http://www.samarinfo.org/donorfaq.asp http://www.samarinfo.org/donorfaq.asp) by South Asian Marrow Association of Recruiters: Marrow donation: Marrow is removed from the bones on one or both sides of the upper hip area using a special syringe. The procedure is performed by an approved collection center, usually under general anesthesia. The entire donation process lasts about one hour. The donor usually spends a night in the hospital for observation. Approximately 3-5% of your marrow is extracted with a syringe and needle. The body naturally replenishes the donated marrow in a couple of weeks. See other questions/answers on the same page for more info.