"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.