Former US President George HW Bush was transferred to hospital in Maine on Sunday for low blood pressure and fatigue, a family spokesman said on Twitter.
Mr Bush, 93, the oldest living former US president, will likely remain at Southern Maine Health Care for a few days for observation, said Jim McGrath.
"The former president is awake and alert, and not in any discomfort," Mr McGrath said.
Last month, Mr Bush was hospitalised for nearly two weeks in Texas for treatment of an infection that spread to his blood. He was admitted to hospital a day after he attended the funeral of his wife, Barbara, the former first lady who died on April 17. The couple had been married for 73 years.
On Saturday, Mr Bush attended an American Legion event in Kennebunkport, Maine to mark the upcoming Memorial Day with military veterans and his former national security adviser Brent Scowcroft, according to a post on Mr Bush's official Twitter feed.
Mr Bush is the father of former Republican President George W Bush, who served two terms from 2001 to 2009, and former Florida Governor Jeb Bush, who unsuccessfully sought the 2016 Republican presidential nomination.
