Doctors say tests prove conclusively that Victor Yushchenko's illness was caused by extremely high levels of dioxin found in the Ukrainian opposition leader's blood and tissue.
Doctor Michael Zimpfer told reporters Mr. Yushchenko had taken food or drink containing high levels of the toxin last September.
"After having completed our examinations which we have conducted in the course of the past 24 hours as well as after having conducted various blood tests there is no doubt about the fact that Mr. Yushchenko's disease has been caused by a case of poisoning based on dioxin," Dr. Zimpfer said.
Dr. Zimpfer said the amounts of dioxin in the blood were found to be over 1,000 times above the normal levels found in the blood supply. Dr. Zimpfer said it would be quite easy to take in such an amount in a bowl of cream soup.
He said the involvement of a third party is suspected but declined to say whether the politician was deliberately poisoned.
Dr. Zimfper added that dioxin stays for a long time in the body so it was possible to identify the toxic.
He said it was possible that more than one type of poison was used but this could never be known for sure.
Dioxin is an industrial agent used as a solvent and was used by the United States during the Vietnam war as a defoliant.
The matter will now be investigated as a criminal case by the authorities in Kiev.
Mr. Yushchenko is expected to return to campaigning there on Sunday or Monday.
Doctors in Vienna say further treatment can be carried out in the Ukraine but the skin disfigurement is likely to stay for years.