Ukraine's parliament is to investigate the alleged poisoning of presidential candidate Viktor Yushchenko, just weeks away from the election.
Yushchenko looked haggard after leaving hospital
Mr Yushchenko is in a close race with Prime Minister Viktor Yanukovich, who is backed by outgoing President Leonid Kuchma in the 31 October poll.
Mr Yushchenko told deputies he had fallen victim to "Ukraine's political cuisine which kills".
He fell ill on 6 September and had hospital treatment in Vienna.
At the time Mr Yushchenko was thought to be suffering from food poisoning.
Journalists reporting on a parliamentary speech he made on Tuesday say he had difficulty speaking, and his face was puffy, red and seemed to be paralysed on one side.
In an angry speech, which was televised, he urged deputies to stand up to the government, warning that they could be next on its list of potential victims.
"I would really like us to receive an answer - who did it and who is the killer? But you know very well who the killer is - the government is the killer!" he said.
He pointed to previous suspicious deaths of political opponents and opposition journalists in President Kuchma's Ukraine.
Foul play denied
Mr Yushchenko's campaign manager Olexander Zinchenko said a medical exam had found evidence of "a viral infection and chemical substances that are not usually found in food products".
In August, an attempt was allegedly made to force the candidate's car off a road as he campaigned in Ukraine.
Mr Yushchenko's campaign team said they had been expecting the authorities to resort to "strong-arm techniques" to ensure the victory of Prime Minister Yanukovich.
However, the deputy head of the Ukrainian presidential administration, Vasyl Baziv, dismissed the claims of wrongdoing.
"I would recommend him to drink a hundred grams of vodka. If he had drunk that nothing would be wrong with him," he said.
Mr Yushchenko is currently ahead of Prime Minister Yanukovich.
However, analysts predict neither candidate will win outright in the first
round, forcing a second round in November.