The mothers of the neighborhood known as Ciudad Oculta refer to them as "the living dead."
They are the emaciated, hollowed-eyed young men, specters huddled in corners, darting in and out of alleys, unconscious in debris-strewn lots and squalid homes behind the walls that earned this neighborhood the name "Hidden City."
Like all children, they once seemed filled with expectations, kicking soccer balls on the windy streets, running off to school with their backpacks, oblivious to the ubiquitous poverty surrounding them.
"So many are lost now," laments Maria Rosa Gonzalez, steering visitors through the shadowy lanes where police seldom venture, just across from the Argentine capital's main slaughterhouse. "The worst is that the youngest face the same fate unless we can change things."
The calamity that has struck the Hidden City and other poor communities of Buenos Aires has a name: Paco, a common male moniker that has acquired a sinister second meaning.
Paco is a potent side-product of cocaine, made from the chemical-laden dregs of the manufacturing process. Experts say it is cheaper, more addictive and more harmful than its comparatively upscale cousin, crack cocaine. Paco contains precious little cocaine, and an abundance of noxious chemicals laced at times with ground glass, dust and other impurities.
Paco is rammed into homemade pipes fashioned from hollow TV antennas, metal tubes, or aluminum foil, with cigarette ash or steel wool serving as heating agents and filters. Handling the scorching pipes burns the fingers and mouths of regular users. They barely notice.
"Once you start smoking Paco, that's all you really care about," says Jeremias Albano, 21, Gonzalez's son, who is detoxing after months of abuse that saw him lose more than half his body weight, leaving him at less than 100 pounds. "You don't sleep. You don't eat. You don't feel the cold. Nothing else matters, just your next Paco."
To feed his habit, Albano stole from his sister and mother and stripped the family refrigerator of metal parts to sell as scrap, he said.
"The only thing of importance to me was getting high," said Albano, who is back to a strapping 190 pounds and appears physically healthy, if disoriented from extensive post-addiction treatment with psychiatric medications. "I didn't care about my mother, my brothers and sister, anything."
There are no accurate figures for the number of Paco addicts here, but officials assure it is in the tens of thousands and multiplying fast. A coalition of community-based groups recently estimated that Paco use in this capital had grown fivefold in the last three years. The problem has overwhelmed treatment and law enforcement capabilities.
"Today, there's not a single [poor] neighborhood where one can't find a dose of Paco," says Sebastian Cinquerrui, a congressman who has studied the issue.
Paco's devastation in the nether regions of Buenos Aires illustrates the secondary damage of the transnational cocaine industry. Law enforcement authorities say Paco's arrival in the streets here reflected the industry's adaptation to enforcement measures.
With its Atlantic port and major international airport, Buenos Aires has long been an important hub for Europe-bound cocaine originating in neighboring Bolivia and Peru, where the coca leaf is grown.
But when crackdowns in Bolivia and Peru reduced availability of chemicals used to produce cocaine, some trafficking organizations moved final production operations to Argentina, which has an advanced chemical industry, a porous border with Bolivia and a notoriously corrupt police force.
"They decided, let's bring the material to Argentina and finish the processing there," said Dr. Jose Granero, director of the federal government's principal drug-fighting agency, known by its acronym, Sedronar.
Soon, dealers learned they could sell the byproduct of their cocaine production to the poor.
Production here takes place on a much smaller scale than in Colombia, Bolivia and Peru, but authorities say it is growing, as evidenced by a sharp increase in the discovery of clandestine cocaine laboratories, known as cocinas, or kitchens.
Dealers and users often serve as lookouts, informing lab bosses of impending raids.
"When the forces of security seek to take down a cocina, they have to first pass by the Paco salesmen on the street," notes Cinquerrui. "By the time they get there, often there's no one and nothing left."
Residents of Ciudad Oculta say the police enter only in force, and traffickers are well warned. The military dictatorship walled off the eyesore district, then known as Barrio General Belgrano, during the 1978 World Cup, increasing its insularity and earning it the designation Hidden City.
South America usually is seen as a producer, not a consumer, of illicit drugs. But authorities say no country on the cocaine trail remains immune.
For years, the youth of Colombia and other coca-growing nations have smoked bazuco, a cheap derivative of cocaine base paste, the first consumable byproduct of the cocaine-production process. Various incarnations of crack cocaine have been a scourge in Brazilian cities since the 1980s.
Paco is cheaper than crack or bazuco, experts say, often costing less than $1 for a "rock" that provides four to five minutes of euphoria. Regular users smoke hundreds of rocks daily.
"I know I'm killing myself," says Ernesto, 29, a jittery paquero from Ciudad Oculta who didn't want his last name used. "But Paco just overcomes me. It's something I can't resist."
The Argentine economic crisis of 2001-02 may have contributed to Paco's rapid growth, officials say. Youths who could no longer afford cocaine or marijuana may have turned to the cheaper and more powerful Paco.
But Paco, experts say, is extremely addictive and toxic. The drug has been linked to numerous cases of brain lesions, respiratory complications and heart attacks, some of them fatal, doctors here say. Irreversible brain damage can occur within six months of intense use, they say.
"Paco generates a very strong addiction and a physical deterioration on the part of the consumers that inevitably leaves them dead in a very short time," concluded a congressional report here last year.
An official here recounted the case of a young girl who died of exposure in downtown Buenos Aires. Paco had dulled her sense of the cold.
Most users are boys who begin smoking as young as 8 or 9, although the early teen years are a more common starting point.
Paco use also has spread to middle-class Argentines, who can order by phone, minimizing direct contact with the demimonde. But mostly Paco remains in the realm of the villas, the poor enclaves where law enforcement presence is minimal.
But mothers soon began casting light into these hidden warrens.
"My son turned into a skeleton," Gonzalez said of Albano. "He was a walking corpse."
She and other mothers called in the police but soon were faced with threats from the drug dealers.
The women were undeterred: They blocked traffic, earning some of the first extensive media coverage of the Paco scourge.
But the path out of Ciudad Oculta has not been easy. Gonzalez was able to check her son into one of the few treatment facilities available. But his condition deteriorated; doctors were giving him 26 different pills a day. Albano was practically a zombie.
"I asked, 'What are you treating the boy with?' " she said. "But the psychiatrist at the clinic never bothered to meet with me."
She placed him in another clinic. He arrived unconscious. She didn't see him for nine days and was terrified. She thought he might be lost.
Albano eventually came through his treatment intact. He has a voracious appetite, although he seems easily agitated. The family has found a subsidized apartment far from the temptations of Ciudad Oculta.
The diminutive homemaker's campaign won Gonzalez some fame as the leader of the "Paco mothers."
Her cellphone often rings with the calls of other despairing parents. She travels from villa to villa trying to help, with little government aid.
Mostly, she just comforts the mothers. Few have the stamina, willpower or time to confront their children, authorities and dealers in what is an exasperating, long-term campaign.
Ciudad Oculta can still be alluring to those who've escaped its walls.
"If I go back inside, I know what will happen," says Ariel Faget, 22, who was raised in the Hidden City. "I'd like to go and see my friends. But I must resist."
Faget describes himself as a former Paco addict who found the will to quit.
"The Paco turned me into a nobody," says Faget, well-groomed and clever, sitting on his bicycle outside the walls of Ciudad Oculta. "To get money, I sold my clothes, I begged for coins on the street.
"But my head is somewhere else now, and I'm doing well. I don't want to go back to that space."
Andres D'Alessandro of The Times' Buenos Aires Bureau contributed to this report.