Kent firefighters and footballers from Gillingham FC were among at least 150 people who gave their time on Thursday to register as bone marrow donors.
Joe's cancer affects just 1% of leukaemia sufferers
A clinic was held at the Just Learning Nursery in Gillingham in aid of a young boy who desperately needs a transplant.
Five-year-old Joe Cawse, from Maidstone, was diagnosed with a rare form of juvenile leukaemia seven months ago and given just two years to live.
Worldwide donor searches have failed to find a bone marrow match for him.
A previous clinic was held in June at his school, West Borough Primary.
Joe needs a complete bone marrow transplant but his mother, Sheriden, said time was running out.
Chris Hope was joined at the clinic by other members of Gillingham FC
"We need to find a donor while Joe is stable and fit and well enough to be able to deal with the huge trauma that a transplant would have on his body," she said.
"We're obviously hoping that we get a match for Joe, but the whole thing about these clinics is to raise people's awareness that there are thousands of people that need bone marrow transplants."
Gillingham defender Chris Hope was one of the many people who gave a blood sample at Thursday's clinic, which was run by the Anthony Nolan Trust.
"I've got two little boys around the same age and when I heard about the story I thought it was sad," he said.
"I just hope they find a right match for him and it all gets sorted out soon, because it's sad to see a little one go through this pain really."
Bone marrow donors must be aged between 18 and 40, weigh more than eight stone (50.8kg) and be in good general health.