HemAssist is the trade name for Diaspirin Cross-Linked Hemoglobin, made by Baxter HealthCare Corp. of Deerfield, Ill. HemAssist is not blood but is made from human blood collected from blood banks after it has become too old for regular uses.

The product is a chemical solution containing large amounts of hemoglobin, the oxygen-carrying protein normally found in red blood cells. Doctors think the product will help save lives in several ways:

• Time would be saved by reducing the need for cross-matching blood tests, which can take up to an hour.

• Unlike whole blood, which cannot be stored longer than six weeks, artificial blood can be stockpiled for six months to a year. That makes it easier to use in emergency rooms, ambulances and disaster relief.

• The particles in artificial blood are smaller than whole blood cells. This may be important in treating traumatic shock, because blood vessels tend to constrict during shock. The smaller particles may help reduce organ damage caused by blood loss by moving farther along tiny blood vessels.

• Artificial blood might be safer. Although blood banks test supplies for AIDS, hepatitis and other diseases, a slight risk remains that a patient will get a contaminated transfusion. Artificial blood is treated to kill viruses, which cannot be done for whole blood.

Doctors say the product cannot duplicate all the benefits of whole blood transfusions. Even if the product proves successful, demand will continue for voluntary blood donations.