More than 7,500 people have offered to become bone marrow donors after hearing of the plight of four brothers who have one of the world's rarest diseases.
The boys are four of only 100 people diagnosed with XLP
Joshua, 12, Nathan, 10, Daniel, eight, and Luke Hartley, four, suffer from X-linked lymphoproliferative disease (XLP), which attacks the immune system.
Most sufferers do not live into their teens, but a transplant may save them.
A testing session for would-be donors is to be held in the boys' home town of Romsey, Hampshire, on Saturday.
The Anthony Nolan Trust, which maintains the register of donors, says it has had an "amazing" response to the appeal made last week.
Spokeswoman Alex Frazier told BBC News Online: "The family themselves are totally humbled and amazed by the response.
"Initially it was very difficult for the family, but the support and help they have received has made a difference to their outlook.
"And the wonderful thing is that the hundreds of donors that have been received may go onto to help one of the thousands of patients across the world in need of transplants."
The Hartley family is expected to make an appearance at the testing session being held at Volumes bookshop in Bell Street, between 1330 and 1630 GMT.
Anyone who is healthy and aged between 18 and 40 can join the Anthony Nolan Trust register and see if they are a match for the boys.
Those interested in joining the register should call 0901 88 22 234 or visit the trust's website. Calls cost 25p a minute.