Hundreds have attended screening sessions to find a stem cell match for a toddler with leukaemia.
One-year-old Phoebe Ashfield, from Gornal, Dudley, needs a transplant to treat a rare form of the illness.
Organisers hoped to collect more than 2,000 samples from the donor drive at two locations in the Black Country on Saturday.
Mother Emma Wyke said it was "overwhelming" to see so many people turn up for her daughter.
Phoebe suffers from Acute lymphoblastic leukaemia, an aggressive condition which affects white blood cells.
About 650 people a year in the UK are diagnosed with the illness, according to the NHS.
Ms Wyke said chemotherapy was not working for her daughter, and doctors at Birmingham Children's Hospital have told the family a stem cell transplant is her best chance for survival.
"If you don't save my little girl's life then you could save another child's life," added Ms Wyke.
The sessions, during which cheek swabs were taken from potential donors, were held at Tesco Extra in Dudley and Tipton Sports Academy.
DKMS, a charity which places people on the stem cell register, co-ordinated the appeal.
"It's a very very simple way of helping to save someone's life," said Kam Arora, a volunteer from the organisation.
Further donor sessions are being planned to help save Phoebe, said her family.
Blood cancer is the fifth most common type of cancer in the UK, according to DKMS.
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