President George W. Bush

"He said he was deeply saddened and would keep Sen. Kennedy in his prayers," spokeswoman Dana Perino said.

Sen. John Kerry, D-Mass.

"Ted Kennedy and the Kennedy family have faced adversity more times, in more instances, with more courage and more determination and more grace than any family should ever have to face even just once.

He's helped millions and millions of people, in so many ways, at so many different times, from countless big pieces of legislation in Washington to the most personal of issues.

Now, everybody needs to pull together on behalf of Ted. We must pull for him and his family and remember that Teddy is one unbelievable fighter.

Over the weekend, I saw him and he's in a fighting mood, and I'm confident that he will continue to draw strength from his tower of strength in Vicki, from each of his children and grandchildren, and from his unbelievably loving and caring family, both in Boston and from his extended family of Americans and people all over the world.

I know that Ted is determined to fight this because he wants to continue his fight for the people of Massachusetts and he wants to continue to fight for everything that he believes in here in the United States Senate and throughout our country.

Teresa's and my prayers -- and the prayers of a nation -- are with my good friend and his family in these most trying of times."

Sen. Barack Obama, D-Ill.

"Michelle and I were saddened to hear the news about Senator Kennedy's condition today, and we plan on doing whatever we can to support him, Vicki, and the entire Kennedy family during this time. Senator Kennedy has been a fighter for his entire life, and I have no doubt that he will fight as hard as he can to get through this. He has been there for the American people during some of our country's most trying moments, and now that he's facing his own, I ask all Americans to keep him in our thoughts and prayers."

Sen. John McCain, R-Ariz.

"Our thoughts and prayers go out to Senator Kennedy and his family. We hope and pray his doctors will be able to effectively treat his condition and that he will experience a full recovery. I have described Ted Kennedy as the last lion in the Senate, and I have held that view because he remains the single most effective member of the Senate."

Rep. Edward Markey, D-Mass.

"Ted Kennedy is the greatest Senator in American history and a tireless fighter for America's families. I know that he will take on this latest challenge with the same fighting spirit, strength and courage he has always shown. My thoughts and prayers are with him, his wife, Vicki, and his family. I look forward to seeing him fully recover and working with him for many, many more years to come."

Sen. Patrick Leahy, D-Vt.

"I'm having a hard time remembering a day in my 34 years here I've felt this sadly."

Sen. Frank Lautenberg, D-N.J.

"We just hope for the best … Ted Kennedy makes the Senate the place that it is and has for so many years."

Former Sen. Bob Kerrey, D-Neb.

"I'm really sad. He's the one politician who brings tears to my eyes when he speaks."

Sen. John Warner, R-Va.

"I am so deeply saddened I have lost the words."

Boston Mayor Thomas Menino, D

"Our thoughts and prayers are with Senator Kennedy and his family. I have faith that my friend will come through this with the same courage he has demonstrated throughout his life. For decades the people of Boston, this nation, and countries around the world have benefited from the Senator's energy, compassion, and commitment to those most in need. We have looked to our senior Senator in the most challenging times and we will continue to fight with him on issues necessary in moving this country forward. On behalf of myself, my family, and the City of Boston, our thoughts are with him and we hope people would respect the privacy of the family during this difficult time."

Democratic National Committee Chairman Howard Dean

"Senator Kennedy is a true American hero and a leader in the Democratic Party, having spent a lifetime standing up for the values of fairness, justice and equality. On behalf of the Democratic Party, we extend our prayers and well wishes to Senator Kennedy, his wife Vicky, and the entire Kennedy family."

Sen. Hillary Clinton, D-N.Y.

"Ted Kennedy's courage and resolve are unmatched, and they have made him one of the greatest legislators in Senate history. Our thoughts are with him and Vicki and we are praying for a quick and full recovery."

Mass. House Speaker Salvatore F. DiMasi, D

"I am deeply saddened by today's news and concerned for the Senator's well being and health and my thoughts and prayers are with the Senator, Vicki and the entire Kennedy family. Ted Kennedy has always been a fighter in Washington for our issues and our Commonwealth and he is my good friend and adviser. I know I speak for all my colleagues in the House when I say we are right behind Ted Kennedy in this fight and, like most other fights in his life, I'm certain he will come out victorious."