Edward Kennedy, one of America's most prominent liberal politician and who suffered seizure Saturday is still in serious condition, but could be out of any immediate danger.
Doctors at Massachusetts General Hospital Sunday were trying to determine the cause of Sen. Edward Kennedy's seizure.
Preliminary tests Saturday night determined the 76-year-old Kennedy had not suffered a stroke, a physician at the hospital said.
Kennedy was flown to the hospital on a medical jet Saturday.
"Over the next couple of days, Sen. Kennedy will undergo further evaluation to determine the cause of the seizure, and a course of treatment will be determined at that time," said Dr. Larry Ronan, Kennedy's primary care physician. He added that Kennedy was "resting comfortably and watching the Red Sox game with his family."
Doctors offered no update Sunday morning.
Well-wishers across the country sent messages to Kennedy and his family.
Senate Majority Leader Harry Reid said Saturday he spoke to the wife of the Massachusetts Democrat, Victoria Reggie Kennedy, and she told him her husband was going to be fine.
"Everyone knows he is a strong fighter," Reid said Saturday, speaking at the Nevada state Democratic Party convention.
Initially, a well-informed, prominent Democratic source in Massachusetts had told CNN that Kennedy seemed to have "symptoms of a stroke."
Someone in the Kennedy compound in Hyannisport called 911 Saturday morning, and an ambulance soon rushed Kennedy to Cape Cod hospital.
He was then flown to Massachusetts General, where he had undergone surgery to remove a blockage in his left carotid artery in October. Kennedy's office said that blockage was discovered "as part of a routine evaluation of Sen. Kennedy's back and spine."
He suffers chronic back pain from injuries suffered in a plane crash in 1964.
In recent days Kennedy has appeared to be in fine health. On Friday, he took part in a ribbon-cutting ceremony for a new maritime learning center in New Bedford.
Family members reported that Kennedy was well enough later in the morning Saturday to call to say he would not be able to join them for lunch.
Kennedy has represented Massachusetts in the U.S. Senate since 1962. He is one of only six senators in U.S. history to serve more than 40 years. He is known as a liberal champion of social issues such as health care, family leave and the minimum wage.
A hospital spokeswoman said he was "resting comfortably and it is unlikely we will know anything for the next 48 hours". Later he was said to be joking with family members by his bedside.
He is the youngest of nine children; his older brothers John F Kennedy, the US president, and Robert "Bobby" Kennedy, a senator, were both assassinated, writes Tony Allen-Mills in Times Online.
Kennedy passed on the torch of his slain brothers to Barack Obama, the likely Democratic presidential nominee. His endorsement of Obama in Washington in January was a hugely symbolic moment at a time when Hillary Clinton was still the Democratic frontrunner.
Kennedy proclaimed that a new era in Democratic politics had dawned, while harking back to a dynasty that predated the Clintons and outshone them in glamour. He has since campaigned tirelessly for Obama.
In 46 years in the Senate he has had great influence as a lawmaker, but his career was tarnished by the Chappaquiddick incident in 1969, when he drove a car off a bridge, killing his passenger, Mary Jo Kopechne, a campaign worker. He received a suspended two-month jail sentence for leaving the scene of an accident.
As a Democratic leader in the US Senate, he has compiled an unrivalled record of legislative achievement and has proved to be one of the last great liberals in an increasingly conservative age, a powerful voice on behalf of America's miserable and misbegotten.
Even after Chappaquiddick he was reelected senator for Massachusetts seven times. He earned the respect of his political enemies, and was once described by Senator Orrin Hatch, a senior Republican from Utah, as "one of the all-time great senators".
He won 10 Democratic primaries in 1980 before bowing out, but the abiding memory of that campaign was his critics' use of a popular song to damn his effort: Simon and Garfunkel's Bridge Over Troubled Water.
While his brothers advanced steadily up the political ladder, Ted attended Harvard University, where he was caught cheating at exams and was expelled. It was the first hint of a flawed, sometimes volatile and frequently contradictory character.
For all his political skills, he is frighteningly prone to moments of appalling judgment, often involving copious quantities of alcohol and - according to some of his biographers - illicit encounters with women.
Kennedy was first elected senator aged 30 in 1962. His brother John had vacated the post when he became president, and a family friend had kept the seat warm until Ted was ready to run.
With hindsight, it may be easy to conclude that he was caught at a weak moment when he attended the fateful party on Chappaquiddick Island off the coast of Martha's Vineyard, home to the Kennedy family estate at Hyannisport. For all the conspiracy theories and wild allegations that the case has generated, Kennedy has been able to secure the loyalty of Massachusetts voters, who never turned against the state's most famous family.
Yet that was not the last of the scandals that have soiled his political record. It was to a Palm Beach bar in 1991 that Kennedy invited his son Patrick and his nephew William Kennedy Smith to join him for a few drinks. The events of that day would ultimately lead to rape charges being brought against Smith in a trial that seriously embarrassed the veteran senator.
What became known as the Palm Beach affair undermined Kennedy's subsequent efforts to block the US Supreme Court appointment of Clarence Thomas, a conservative black judge who had been accused of sexual harassment.
Although Smith was acquitted and Kennedy was never accused of breaking any law, he later felt obliged to offer a kind of apology for his failings. "I recognise my own shortcomings - the faults in my private life," he said in late 1991. "I realise that I alone am responsible for them and I am the one who must confront them."
The following year he married his second wife, Victoria, who is said to be a calming influence.