Tests show the level of poison in the blood of Ukraine's Viktor Yushchenko is more than 6,000 times higher than normal, an academic has said.
Yushchenko blames poison for his sudden facial disfigurement
Prof Abraham Brouwer at the Free University in Amsterdam, who carried out the tests, said it was the second highest level ever recorded in humans.
The presidential candidate, who faces PM Viktor Yanukovych in a repeat poll on 26 December, fell ill in September.
Doctors in Vienna said last week dioxin poison disfigured Mr Yushchenko's face.
Blood samples taken last week in the Austrian capital were sent to Amsterdam in the Netherlands for further analysis.
Mr Brouwer, a professor of environmental toxicology, said the record concentration found in Mr Yushchenko's blood was about 100,000 units per gram of blood fat.
He is hoping to identify the exact form of the poison by the end of the week.
"The labs will... try to find out whether it matches any of the batches of dioxins that
are around, so that maybe you can trace it back to where it was ordered or where it came from," he told the Associated Press news agency.
The highest level ever is thought to have been found in two women in Vienna in the 1990s, Prof Brouwer told the BBC News website, but said he did not have any more information on the case.
The two women worked at a textile institute and had levels of dioxin in their systems thousands of times higher than normally found, Olaf Paepke, a scientist at a Hamburg institute who conducted chemical analysis for the investigation, is reported as saying by the Washington Post newspaper.
It was never determined how the employees, who survived, had been poisoned.