The decision by a parliamentary commission followed a similar move by the country's prosecutor general on Sunday. The commission will be led by Volodymyr Sivkovych, a lawmaker who has supported Prime Minister Viktor Yanukovych, Yushchenko's opponent in the Dec. 26 rerun for the presidency.
"The results of the most recent expertise in Vienna are giving us grounds to renew our work," Sivkovych said. "However, we are not convinced that deliberate poisoning can be proved."
Yushchenko is a front-runner in a runoff ballot that is to take place in less than two weeks, reports CBS News Correspondent Sheila MacVicar. It's been a dirty election, with voting marred by fraud, intimidation, and now, doctors say, evidence of a murder plot. Yushchenko says he knows who is behind it and points his finger at the current government.
An earlier commission led by Sivkovych investigated the case in October and decided that Yushchenko suffered a combination of a viral infection and several other diseases.
Dioxin is the most active animal carcinogen known to mankind, so Yushchenko runs a high cancer risk, Dr. Marc Siegel, an associate professor of medicine at New York University, told CBS News Early Show Co-Anchor Harry Smith.
Yushchenko was tested for poisoning shortly after he developed stomach ulcers and debilitating back pain. However, says Siegel, he was not tested for dioxin, partly because the telltale adult acne lesions didn't appear right away.
Prosecutors had closed the investigation before the Nov. 21 second round of voting, saying that they could not determine whether he was poisoned, but now they have reopened it.
Sivkovych urged Yushchenko to immediately hand over results of the tests conducted by doctors in Austria to prosecutors and the parliamentary committee.
Yushchenko praised Ukraine's prosecutor general Sunday for reopening the criminal investigation into his illness, but said that he hoped the investigation would be conducted after the rerun because he didn't want the vote to be influenced "either positively or negatively" by the inquiry.
Election officials, meanwhile, geared up Monday for the third round of voting in Ukraine's bitterly fought presidential election, scheduling a lottery for the allotment of TV airtime between and Prime Minister Viktor Yanukovych.
Terry Davis, the secretary general of the Council of Europe, Europe's top human right's body, traveled to Kiev to discuss the preparations for the Dec. 26 balloting, which the Supreme Court ordered after determining last month's second-round vote was fraudulent. Davis was scheduled to meet with outgoing President Leonid Kuchma, other top officials, Yanukovych and Yushchenko.
Doctors at Vienna's Rudolfiner clinic said tests run over the weekend proved beyond a doubt that it was dioxin poisoning that caused a mystery illness in September that left Yushchenko disfigured and in pain.
"This question will require a great deal of time and serious investigation. Let us do it after the election — today is not the moment," Yushchenko said in Vienna on Sunday.
While high concentrations of dioxin, a byproduct of industrial processes, remain in his blood, doctors said Yushchenko's organs have not been damaged and he is fit for the campaign trail.
Lawmakers from Yushchenko's party said the clinic's findings confirmed that his opponents wanted to assassinate or disable him rather than take the risk he would defeat the Kremlin-backed Yanukovych in the presidential election.
Yushchenko fell ill Sept. 5 and has been treated at the Vienna clinic twice before.
In Las Vegas, Ukraine's top boxing star, Vitali Klitschko, dedicated his latest victory Saturday, over Danny Williams, to the people of Ukraine and their struggle for democracy.
"I hope this fight supports people who fight ... for democracy," Klitschko said after defending his heavyweight title.
He wore an orange flag on his trunks during the match to signal his staunch support for Yushchenko.