South Korean scientist Hwang Woo-suk’s groundbreaking stem cell research was cast into fresh doubt Tuesday as a former collaborator said he provided hundreds more human eggs than Hwang claimed to have used, a report said.

Roh Sung-il, chairman of the board at Seoul’s Mizmedi Hospital, said the hospital provided over 900 eggs from 65 people for a paper Hwang published in the journal Science this year.