AP has a scary story on Yushchenko's poisoning, by Emma Ross, AP Medical Writer:

LONDON - New tests reveal Ukrainian presidential candidate Viktor Yushchenko's blood contains the second-highest level of dioxin poisoning ever recorded in a human — more than 6,000 times the normal concentration, according to the expert analyzing the samples.

Abraham Brouwer, professor of environmental toxicology at the Free University in Amsterdam, where the blood samples were sent for analysis, said they contained about 100,000 units of dioxin per gram of blood fat.

However, the concentration could prove to be even higher, or lower, once results are in later this week from a more definitive test, said Arnold Schechter, a specialist in dioxin analysis from the University of Texas Southwestern Medical Center in Dallas.

[...]

Schechter said it also could determine that Yushchenko was poisoned with dioxin-like PCBs, rather than dioxins. PCBs were used in electrical transformers and as hydraulic fluid until they were banned in much of the world in the 1970s because they are so toxic and persist so long in the environment.

Brouwer's team has narrowed the search from more than 400 types of dioxin to about 29 and is confident they will identify the poison by week's end. That, in turn, could provide clues to its source.

"From a (chemical) fingerprint, at least you can deduce what kind of sources might have been involved," Brouwer told The Associated Press. "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."

[...]

"It was very late before the rash started to develop, so if he had died it would have been a mystery illness of his pancreas, his liver or his gut and they would have said maybe it's some rare bug thing," said John Henry, a toxicologist at London's Imperial College. "He would have died within a few days and nobody would ever, ever have thought of dioxins."

[...]

It would not be difficult to deliver the dose Yushchenko received, experts say. If the dioxin he ingested is the most hazardous type, tetrachlorodibenzoparadioxin, or TCDD, it would take only a drop or two, or a tiny amount of powder mixed in food, to poison him.

Most of what is known about the health effects of acute dioxin poisoning comes from experiments on animals. Most animals would die from the levels in Yushchenko's blood.