Since the mid-1980s, an estimated 7 million Americans -- including athletes, burn victims, cancer patients and seniors -- have received transplant tissue. Exact numbers are elusive since the Food and Drug Administration only recently began taking inventory. "Nobody really tracks the transplant side," says Robert Rigney, CEO of the American Association of Tissue Banks.

Here are the tissues most commonly harvested and some of the main uses to which they're put:

* Musculoskeletal tissue, including bones and tendons: Used to repair parts damaged by trauma or disease. There were some 875,000 musculoskeletal grafts in 2001, according to the National Center for Health Statistics.

* Skin: Used primarily as a dressing for patients with large burns. Grafts help prevent fluid loss, protect the patient from bacterial infection and decrease pain. Transplanted skin tissue also is used for some cosmetic procedures. The National Center for Health Statistics reports 20,000 skin grafts in 2001.

* Corneas and scleras: Used to restore vision after trauma or disease, such as glaucoma. More than 33,000 corneal transplants were conducted in the United States in 2001, according to the Eye Bank Association of America.

* Bone marrow, taken from the breast bone, ribs, hip bones, skull and spine: Used to treat diseases of the immune and blood systems, some pediatric genetic disorders and cancer. An estimated 1,560 bone marrow transplants are performed annually, according to the National Marrow Donor Program.

* Heart valves and saphenous veins (either of two leg veins): Used in the repair of diseased or damaged veins. More than 60,000 valve replacements are performed annually, according to the American Medical Association Council on Scientific Affairs.

For more information on local organ and tissue donation programs:

* The Organ Donation Transplant Network maintains the only national patient waiting list. 888-894-6361; www.optn.org/.

* The Washington Regional Transplant Consortium coordinates organ, tissue and eye donation in the Washington area. 866-232-3666 (866-Be-A-Donor), 703-641-0100; www.wrtc.org.

* The U.S. Department of Health and Human Services promotes organ donor programs nationwide. 301-443-7577; www.organdonor.gov.

-- Rita Zeidner