Former US President Gerald Ford has been taken to hospital in Minnesota for unspecified "testing and evaluation".
Mr Ford, 93, was admitted to the Mayo Clinic in Rochester, about 75 miles (120 kilometres) south-east of Minneapolis, his office said.
It is the fourth time since last December that the former president has been admitted to hospital.
"No further releases or updates are anticipated prior to early next week," his office said in a statement.
Mr Ford remains the only US president never to have contested a national election before entering office.
As vice-president, he became president in 1974 when Richard Nixon resigned because of the Watergate affair.
But he failed to win a full term in the 1976 presidential election, losing to Democrat Jimmy Carter.
Mr Ford became the nation's oldest living former president after the death of Ronald Reagan in 2004.
Last month, he spent a few days in Colorado's Vail Valley Medical Center because of shortness of breath.
In January, he was taken to hospital in California, suffering from pneumonia. And in December 2005, he went to the same hospital to be treated for a bad cold.
Mr Ford suffered two small strokes five years ago and spent about a week in a hospital.
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