The board received the half-page official withdrawal paperwork Thursday morning, five weeks after Ryan abandoned the race because of sex club allegations in his divorce from television actress Jeri Ryan, star of "Boston Public" and "Star Trek: Voyager."
Ryan's withdrawal clears the way for the Illinois Republican Party to name a replacement candidate to face Democratic state Sen. Barack Obama. The state GOP could not have forced Ryan off the November ballot for the open seat of retiring Republican Sen. Peter Fitzgerald.
Some backers said Ryan got bad advice and should not have dropped out.
Dairy owner Jim Oberweis, runner-up in the March primary, retired Air Force Gen. John Borling and Cook County Commissioner Liz Dooty Gorman are being mentioned as likely candidates, WLS-TV, Chicago, said.