Questions over the suspected dioxin poisoning of Ukrainian opposition candidate Viktor Yushchenko filled the international media over the weekend, particularly in the United States and Moscow, where the election in Ukraine is seen less as a reflection of domestic politics than as a referendum on the future Russian sphere of influence. Particularly mysterious is the determination that the alleged poisoning, which occurred months before the election, was caused by dioxin. Dioxin in the environment is a byproduct of the incineration of chlorinated compounds; forest fires are the world's largest source of dioxin, but even a forest fire will precipitate only a few molecules of the substance. It is measured in parts per trillion outside incinerators and certain industrial plants, and total industrial emissions in the United States can be measured in grams or tablespoons. Dioxin also is created as a byproduct in certain chemical manufacturing, and is found in the Vietnam-era defoliant Agent Orange. Dioxin is present in the environment in varying concentrations, and can build up in the fatty tissues of people exposed to it. When people talk about negative health effects from dioxin, they are generally referring to a long-term build up of dioxin in the body causing certain cancers and birth defects. Agent Orange is dioxin-laden, and soldiers in Vietnam responsible for spraying Agent Orange — in Operation Ranch Hand — have been the best study group for scientists, but few from Operation Ranch Hand showed signs of acute exposure. Despite having a large group exposed to dioxin in small doses over many months, there still is much debate over just how dangerous long-term exposure to dioxin might be. Yushchenko shows signs of acute exposure, with characteristic chloracne seen vividly on his face. Poisoning with a form of dioxin is a rather complex manner of trying to eliminate a competitor from an election. There are many more readily available, more lethal and less identifiable poisons available, particularly in the arsenals of former Soviet states. This has raised speculation in Russia and Ukraine that Yushchenko's poisoning was not perpetrated by his opponents, but by shrewd players in his own camp interested in adding to the sense of embattlement and painting the ruling party in the worst possible light — by choosing a poison that was easily identifiable and that would leave vivid marks but have a minimal chance of resulting in death or lasting incapacitation. That such speculation is once again coming to the fore as the presidential re-vote nears raises further suspicions about the nature and source of the poisoning. But even this raises questions about the use of dioxin. It is a rather unusual choice for a poison, and the consequences of acute exposure are unclear, particularly in the long term. That a political figure might be willing to become a guinea pig and risk his own health and life for a shot at turning a few votes or gaining international sympathy for an election seems extreme. There are relatively solid arguments being bandied about that Yushchenko's competitors or his supporters are responsible. The unmentioned alternative is that Yushchenko was the victim of accidental poisoning, perhaps through his water supply or some other acute exposure. But the lingering question of poisoning raises the specter of the bad old days of the Cold War when both sides used whatever means necessary to affect events in proxy and contested states. Whether the Ukrainian election represents the resurgence of Moscow's attempts to balance the steady encroachment of the West through the old Iron Curtain and into the former Soviet states, or whether it instead marks the death knell for Moscow's influence and control in nearby states, will not be clear for months. Either way, the election in Ukraine — re-vote, alleged poisoning and all — looks to be an historical point in the saga of Russo-U.S. relations.