The president is to undergo the screening Saturday at Camp David, the presidential retreat in Maryland, CNN reported. White House spokesman Tony Snow, who recently announced that his cancer, which began in his colon, has recurred, said the procedure is expected to take about 2 ½ hours.

Cheney is to be acting president while Bush is under anesthetic.

Bush's last colonoscopy was in 2002. The screening is considered the most reliable one for colon and rectal cancer and for polyps that can become cancerous.