NHS Blood and Transplant (NHSBT) is asking people who have recovered from Covid-19 to donate their blood so they can assess the therapy in trials.
The hope is that the antibodies they have built up will help to clear the virus in others.
The US has already started a major project to study this, involving more than 1,500 hospitals.
When a person has Covid-19, their immune system responds by creating antibodies, which attack the virus.
Over time these build up and can be found in the plasma, the liquid portion of the blood.
