The "Good Morning America" anchor is being treated for MDS, a blood and bone marrow disease. She will require a transplant this fall.
Roberts stopped by a registration drive at ABC News on Tuesday, watching co-host George Stephanopoulos and her boss, ABC News President Ben Sherwood, get swabbed to see if their bone marrow is a match for someone who needs a donation.
Jeffrey Chell, CEO of the registry Be The Match, said some 15,000 people had registered since Roberts announced her diagnosis on June 11. That's 11,200 more than they would normally receive in that period.