If Don Flounders waits for the asbestos-related mesothelioma that is ravaging his lungs to kill him, it will be a slow, painful death.
But one day -- maybe just weeks away and at the moment of his choosing -- the 78-year-old plans to drink a bitter mixture of alcohol and pentobarbital, a barbiturate that is used to euthanize pets.
Flounders told ABCNews.com that he flew halfway around the world from his native Australia to obtain the illegal drug in Mexico, which, like Switzerland, is fast becoming one of the recommended destinations for so-called death tourists.
The lethal drug, once widely available in the U.S. as a sleep aid and now used primarily in veterinary medicine, was an ingredient in the fatal cocktails that killed Marilyn Monroe and Judy Garland in the 1960s.
Since 2001, the pro-euthanasia group Exit International has helped nearly 300 people -- mostly Australians, New Zealanders and a handful of Americans -- to find what is being called "death in a bottle" in pet pharmacies in Mexico.
Commonly known as Nembutal, this concentrated drug will put Flounders to sleep quickly and quietly, by taking his breath away.
"I had no trouble whatsoever purchasing the poison," said Flounders from his home near Melbourne. "It will be completely painless. Of the various means, this is the easiest and most reliable. It's a way of achieving a peaceful death."
He will take the Nembutal with a glassful of his "favorite tipple" -- gin. "You swig it down and I'll just close my eyes," he told ABCNews.com. "It's that rapid."
Exit International's Web site says the best places to obtain pentobarbital are "20-odd [United States-Mexico] border crossings, from Tijuana in California through to Matamoros on the Gulf of Mexico."
The group provides information packets for these death tourists, with colorful photos of the packaging to help identify the drug among all the animal products for sale in these over-the-counter veterinary stores.
"There aren't that many drugs that a doctor can give you for a reliable, peaceful death," said Exit's founder and director Philip Nitschke.
"It's always drunk quickly," he told ABCNews.com. "I've never seen anyone finish their whiskey or French champagne."
Nitschke co-authored "The Peaceful Pill Handbook," the Australian version of the 1991 American Hemlock Society guide, "Final Exit," which lays out precisely how to end your life. The book is banned in Australia, where assisted suicide is now illegal.
"People know we are sympathetic," Nitschke told ABCNews.com. "We are drowning in patients coming along who are in dreadful trouble and say, 'Help us die.'"
Flounders learned about Nembutal from Exit International. He and his wife, Iris, had become members a decade before he was diagnosed with terminal cancer.
For 16 years, Flounders worked as an executive for Shell Oil in Melbourne, but he has since learned he had been working in a building contaminated with blue asbestos -- "the worst kind," he said.
Since then, his condition has worsened. Just this week, the couple was waiting for an ambulance to take him to the hospital for new tests because of excruciating back pain. Iris, who is 85, bought her own supply of Nembutal in Mexico and says she, too, might take her life at the same time. Iris says she does not have a terminal illness.
The couple have been married for 57 years and have two grown children who have been supportive of their decision.
"We are perfectly happy to go with no reluctance on our part," he said.
Australian television crews followed the Flounders across the border from California into Mexico, where they bought enough supplies for themselves and a dying friend and Exit activist, Anjy Belecciu.
Belecciu, who is 56 and dying of metastasized breast cancer, helped finance the trip because her bones are too brittle to travel.
The Flounders bought several 100 milliliter bottles of the sterile, liquid pentobarbital for under $50 each.
"People are comforted with the way it is packaged with an expiration date in the future and the seal intact," said Nitschke. "There is no evidence of a black market."
But Robert Merrill, a Mexican-American veterinarian who practices in San Miguel de Allende, said it is illegal to sell the drug to death tourists and such an action raises ethical questions.
"I would hope that pentobarbital is only sold to licensed veterinarians," he told ABCNews.com "But then the licensed veterinarians have to decide what their moral issues are and who they will sell it to."
San Diego border agents told ABCNews.com that they had not confiscated pentobarbital at their busy crossing, where they see plenty of other animal drugs, like anabolic steroids and the "date rape" drug ketamine, smuggled in for human consumption, said Vincent Bond, spokesman for U.S. Customs and Border Protection.
Press reports in Mexico and the U.S. say veterinary pharmacists were surprised at the increased interest in Nembutal.
"We didn't have any idea what they were doing," one Tijuana sales clerk told The New York Times in a recent report. "It's for animals. Everything here is for animals. We thought they were giving it to their animals."
Six days after their highly publicized return, federal and state police raided both the Flounders' and Belecciu's homes, hoping to arrest them, but no drugs were found.
"There are a lot of rabbit burrows on my property," said Flounders, who still retains his good humor.
If Belecciu takes her life first, Flounders can be charged with assisted suicide. So, too, can she be charged if he goes first -- a crime that carries a 14-year jail sentence in Victoria, the state where both live.
"Suicide is not a crime," said Nitschke. "It's only a crime if someone helps you."
Assisted suicide is legal in Switzerland, the Netherlands and Belgium, where a pentobarbital-based elixir is often used.
For about eight months, it was legal in the remote Northern Territories of Australia. There as a general doctor, Nitschke helped with the lethal injection of four of his patients until the law, similar to one in Oregon, was overturned by Parliament.
Using Nembutal for assisted suicide is not as common in the U.S., according to Dr. Bruce Goldberger, director of toxicology at the University of Florida College of Medicine.
"The typical final exit case would be a mixture of drugs and a bag over your head," said Goldberger, who investigates more than 3,000 homicides, suicides and accidental deaths a year.
He said a gas like helium can be bought at Wal-Mart.
"What prevents someone from overdosing on their medications that are routinely given from a physician?" he asked. "All you have to do is mix it with alcohol."
But Nembutal is "comfortable and reliable," according to Goldberger. Using a cocktail of prescription drugs may not work as quickly and can fail and cause brain damage.
What puzzles the Australian death tourists is why more Americans, who are so close to the border, don't take advantage of the easy availability of Nembutal.
"In the U.S., at least the middle and upper classes who can afford to travel usually work out some sort of behind-the-scenes arrangement with their doctor," said Dr. Art Caplan, director of the center for bioethics at the University of Pennsylvania.
"I write a prescription and you are not to take more than 30 pills," he said. "Doctors warn people, but there is a lot of winking and nodding."
Americans also use "guns and bridges," according to Caplan, who said typically doctors -- even in cases of the terminally ill -- try to avoid suicides and counsel on pain control and emotional support.
"As a culture, we seem to think that the medical way is better," he said. "Our society strongly condemns assisted suicide."
But Barbara Coombs Lee, president of Compassion and Choices, a nonprofit organization that works to improve care and expand choice at the end of life, said "desperate and determined" people will travel the globe to find a "peaceful and humane way out."
"Many people fear getting stuck in a prolonged and degrading process," she told ABCNews.com, but crossing the border to buy drugs designed for pets may not be the safest alternative.
"Ask any woman," she said. "The back alley is a dangerous and degrading place to get medical care. It used to be the VW bus and Dr. Kevorkian. Now it's the vet pharmacy."
Meanwhile, Don and Iris Flounders say their decision was made of sound mind and not in haste.
"It has to be well controlled, or everyone is going in to the chemist [pharmacist]," he said. "It's for people who have seen their doctor and have been thoroughly examined and mentally tested and cleared."
For them, knowing they have the Nembutal -- just in case Flounders' pain is out of control and his family is suffering -- gives them peace of mind.
"You don't feel the need to use it nearly as much as the longing for it," he said. And bringing back a dose for his friend has also given him comfort.
"Anjy said before, she resented dying," Flounders said. "Now, she says, 'You have given me life.' She didn't have a choice before."
The expensive and arduous trip to Mexico was "worth it," he said. And Flounders has not changed his mind about taking his life when the time is right.
"We are quiet-living people and not excessively excitable," said Flounders. "I'm the one who got the death sentence, but it doesn't worry me. As far as I'm concerned, I've had a good life."
ABC News' Karin Halperin in Mexico and Cloe Shasha and Gerard Middleton in New York contributed to this report.