Senator Edward Kennedy, who is being treated for brain cancer, has been taken to a hospital near his Cape Cod vacation home after complaining of feeling ill.
Sergeant Ben Baxter, a police officer, said an emergency call from the Kennedy compound in Hyannis Port came about 5 pm (21:00 GMT) on Friday.
Baxter said that Kennedy, 76, was conscious and responsive when he was picked up by an ambulance.
His office later confirmed that "Senator Kennedy experienced a mild seizure at home in Hyannis Port today and was taken to Cape Cod Hospital for examination."
"Doctors believe the incident was triggered by a change in medication. Senator Kennedy will return home tonight and looks forward to watching the (presidential) debate," the office said in a statement.
Kennedy had a seizure in May and underwent surgery in June for a malignant brain tumor.
The longtime senator and patriarch of America's most fabled political family was diagnosed on May 17 with brain cancer.
He made a dramatic appearance at the Democratic National Convention in Denver last month in support of Democratic presidential candidate Barack Obama.