BOSTON (Reuters) - Sen. Edward Kennedy, a leading Democrat, suffered a seizure on Saturday but hours later was talking with family at his side in a Boston hospital.
Kennedy, 76, was rushed from the family vacation compound at Hyannisport, Massachusetts, to Cape Cod Hospital at 9 a.m., before being airlifted to Boston.
"He is undergoing a battery of tests at Massachusetts General Hospital to determine the cause of the seizure," his office in Washington said in a statement.
A Kennedy aide said later that by Saturday afternoon the senator was joking with family members.
Senate Democratic Leader Harry Reid, after talking with Kennedy's wife, Vicki, told reporters in Reno, Nevada, that the senator "will be fine," a Reid aide said.
Reid said the senator had a seizure, but "woke up fighting," the aide added.
The Boston Globe reported Kennedy, youngest brother of assassinated President John F. Kennedy, suffered one seizure at his Cape Cod home and a second seizure aboard the helicopter transport flight to Boston.
Family members gathered at the hospital. His sons Edward Kennedy Jr. and Patrick and daughter Kara as well as his nephew Joe Kennedy and niece Caroline Kennedy came to the hospital, according a Reuters photographer at the scene.
Kennedy, the second-longest serving member of the current U.S. Senate, is a leading liberal voice in the United States and has actively campaigned for Barack Obama in his bid to become the Democratic nominee in the November presidential election.
"As I've said many times before, Ted Kennedy is a giant in American political history. He's done more for the health care of others than just about anybody in history," Obama told reporters during a visit to a hospital in Eugene, Oregon.
"We are going to be rooting for him, and I, I insist on being optimistic about how it's going to turn out."
Campaigning in Kentucky, Sen. Hillary Clinton, Obama's rival for the Democratic nomination, offered her wishes for the senator's quick recovery.
Kennedy has been a vocal critic of Republican President George W. Bush, particularly on his Iraq war, tax cuts for the wealthy and conservative nominees to the U.S. Supreme Court who he fears will push the high court to the right.
But he also worked closely with Republicans on legislation including Republican presidential candidate John McCain on the controversial immigration issue.
"He is a legendary lawmaker," McCain said in a statement. "When we have worked together, he has been a skillful, fair and generous partner. I consider it a great privilege to call him my friend."
The white-haired senator has had other brushes with ill health. He had preventive surgery at Boston's Massachusetts General Hospital in October to unclog a partially blocked carotid artery in his neck.
The blockage was discovered during a routine check of Kennedy's back and spine, doctors said. A blocked carotid artery can lead to a stroke and death, they said at the time.
Kennedy has suffered from back problems since a plane crash in 1964 in which the pilot and one of Kennedy's aides were killed and the senator was pulled from the wreckage with a punctured lung, broken ribs and internal bleeding.
Kennedy came to the Senate in November 1962 to fill a seat earlier held by his older brother, then President John Kennedy. He currently serves as chairman of the Senate Committee on Health, Education, Labor and Pensions.
He ran for president in 1980, but his White House ambitions had never recovered from Chappaquiddick, the July 1969 accident when his car plunged off a bridge on a Massachusetts island and a young woman riding with him, Mary Jo Kopechne, drowned. Kennedy lost the 1980 party nomination to Jimmy Carter who failed in his bid for a second White House term.
Kennedy helped win an increase in the national minimum wage this year and worked with Republicans to produce broad immigration reform, which failed in the Senate after stiff opposition from conservative Republicans.
His oldest brother, Joseph Jr, died as a World War II flier when his bomber exploded over the English Channel. John became America's first and so far only Roman Catholic president in 1960 and was assassinated in 1963. Robert was assassinated during his 1968 presidential campaign.
Additional reporting by Thomas Ferraro, Charles Abbott, and Doina Chiacu in Washington, Jeff Mason in Eugene, Oregon, and Caren Bohan in New York; Writing by Jason Szep. Editing by Jackie Frank