Like other teens, Sara had experimented with drugs, and had recently confided to her mom that she liked to smoke pot every once in a while. That worried her mother. But Sara had a job and a wide circle of friends, and was just a few weeks from high school graduation. All in all, she seemed OK. Aeschlimann thanked her daughter for calling and hung up.

A short time after the call, as Sara was watching TV and playing pool in Harth's basement, he reportedly offered the striking blond, brown-eyed girl a potent brand of ecstasy known as "double stack white Mitsubishi." She had apparently taken ecstasy for the first time a couple of months earlier, and the round white pills were supposed to be the hottest version of ecstasy around. She washed down a few and waited for the drug's effects to kick in.

Indeed, they did. Within hours, she was in convulsions and had to be rushed to the hospital. There, she lapsed into a coma and her body temperature rose quickly, not stopping until it reached 108 degrees. "She was bleeding everywhere," says her mother. "Her blood cells were just erupting. Her intestines were bleeding; her stomach was bleeding. She was bleeding from the mouth. She bit her lip when she had a seizure, and it wouldn't stop bleeding, but she was not moving at all."

By 3 the next afternoon, Mother's Day, she was dead. Instead of taking methylenedioxymethamphetamine (MDMA), the only chemical contained in unadulterated ecstasy, she had unknowingly swallowed paramethoxymethamphetamine, a much more dangerous chemical known as PMA. The DuPage County coroner's office determined that Sara died from an accidental overdose of PMA, a substance also believed to be responsible for at least two other recent deaths in the Chicago area.

Contaminated illegal drugs have never been a big issue in the United States. But if the demand for ecstasy continues to rise, as some researchers speculate it will, more and more dealers may start substituting deadly substances like PMA for less harmful drugs like MDMA.

"The ingredients for MDMA are highly controlled, and you have any number of people willing to make substitutes that are much more dangerous," says Dr. David Nichols, professor of medicinal chemistry and molecular pharmacology at Purdue University and one of the few to ever study the effects of PMA. "If you make one drug illegal, it will be replaced by a more dangerous drug. No matter how much you try to control it, people will come up with substitutes."

With the skyrocketing demand for ecstasy and its low production outlay -- it costs only 10 to 50 cents to make a pill that sells on the street for $20 to $45 -- there is a compelling economic incentive to sell the drug even if it's entirely made of another substance. "The rave scene is a huge market of people willing to pay $20 or $30 per pill to get high, and a lot of people are taking advantage of it," Nichols says.

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