Senator Edward Kennedy, who is being treated for brain cancer, has been taken back home to Cape Cod after being rushed to a Massachusetts hospital in an ambulance after complaining of feeling ill.
A statement issued by the 76-year-old senator's office attributed the episode on Friday to a change in medications.
The statement said Kennedy returned home after spending at least three hours in the hospital.
Earlier 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.