The 61-year-old former Missouri senator canceled an appearance Thursday afternoon, believing at the time that he had the stomach flu, said Justice Department (search) spokesman Mark Corallo. But Thursday night, Ashcroft was admitted to George Washington University Hospital (search) for tests.
"He went home and when the condition worsened, he was visited by White House physician Daniel Parks, who advised that he go to the emergency room," Corallo said.
"After a full medical work-up in the emergency room, it was determined that he was suffering from a severe case of gallstone pancreatitis," Corallo said. "He was admitted to intensive care for careful monitoring and is being treated with antibiotics."
Corallo said he expects Ashcroft, who has not had any prior health problems, will spend a couple of days in the hospital.
President Bush called Ashcroft on Friday and spoke briefly with him and Mrs. Ashcroft. Bush told them that his thoughts and prayers were with them, government sources said.
Pancreatitis is an inflammation of the pancreas usually caused by excessive alcohol use or, as in Ashcroft's case, a gallstone that blocks the passage leading from the pancreas to the beginning of the small intestine. It also may be caused by infection, injury or certain medications.
Symptoms include sudden, severe abdominal pain, loss of appetite, nausea, vomiting and fever.
In 85 to 90 percent of patients, acute pancreatitis resolves completely in three to seven days after treatment is instituted. Medical therapy is aimed at reducing pancreatic secretion, thereby "resting" the pancreas, and usually involves intravenous fluids and eliminating oral intake.
Ashcroft canceled a Thursday afternoon event in which he was to have announced verdicts in a terrorism case.
Fox News' Anna Stolley and The Associated Press contributed to this report.