Yushchenko in Austrian hospital for tests

Ukrainian presidential candidate Viktor Yushchenko checked into an Austrian hospital to undergo new tests, and doctors said they wanted to re-examine him to assess whether his mysterious illness was caused by poisoning.

"He needs to be re-examined so that we can get a chance to further clarify the nature of his illness," Dr. Michael Zimpfer, director of the Rudolfinerhaus hospital, told reporters shortly after Yushchenko's arrival late Friday.

"It will be an entire imaging diagnosis to look at the size and function of his various organs. We are going to reassess the entire blood chemistry, including possible types of poisoning. We will take tissue biopsies and we will work from this."

Zimpfer said the biopsies would be taken from "wherever is necessary, including his skin and the mucus of his bowels."

Yushchenko has accused Ukrainian authorities of trying to poison him in the run-up to November's fraudulent presidential election. Ukraine's Supreme Court voided the outcome after Yushchenko lost to Prime Minister Viktor Yanukovych, and a rerun of the ballot will be held on December 26.

He first fell ill in September and was rushed to the Vienna hospital. He resumed campaigning later in the month but with a pockmarked and badly disfigured face.

"Actually, he was very lucky that he was brought to Vienna because doctors said if he would stay another 24 hours in Ukraine, it could be a 'final solution,' so called," Oleh Rybachuk, Yushchenko's chief of staff, said in a televised interview Friday night for the "NewsHour with Jim Lehrer" on U.S. public television.

"And now after taking two treatments in Vienna, he has fully recovered, as (the) doctor says, but he needs a certain rest and he needs to take care of this effects on his face which they call residual. But actually, internally there are no more damages so he has been cured internally," Rybachuk said.

If Yushchenko's disfigurement turns out to be chloracne - a type of adult acne caused by exposure to toxic chemicals - it could take a long time to clear, Zimpfer said. Sometimes it takes two to three years for people to heal.

Yushchenko told reporters on arrival Friday that he would stay until Monday, unless tests were finished before then.

He arrived in a convoy of three cars, surrounded by bodyguards, and was accompanied by his wife, Kateryna Chumachenko.

"Everything is going well. I plan to live for a long time and I plan to live happily. I am getting better health every day," said Yushchenko, wearing a scarf in his orange campaign color.

Zimpfer said doctors "cannot exclude poisoning," but added: "Theoretically it could be that we never can prove poisoning because he only came here a few days after the symptoms appeared. On the other hand, there are poisons that stay in the body a long time."