How Ready Are We for Bioterrorism? A few days after 9/11, a retired Air Force colonel named Randall Larsen entered the northwest gate of the White House, crossed a courtyard to the Eisenhower Executive Office Building, stepped through the front door and stopped dead in his tracks. Richard Burbridge for The New York Times BE PREPARED Are we ready for a biological attack? Probably not. In place of the usual security checkpoint, there was an elaborate upgrade that included not only metal detectors but also machines to sniff out radiation and explosives, elaborate pat-downs and a mandatory search of all personal belongings. It was the search that worried Larsen most. After passing through a body scan, he stood quietly while a guard thumbed through the contents of his briefcase. It was mostly books and papers, but after a few seconds, the agent pulled out a respirator mask and shot Larsen a quizzical look. "That's just for demonstration," Larsen said quickly. You saw Mayor Giuliani wear one at ground zero, right? The agent turned the mask over a few times, then stuffed it back in the briefcase. Seconds later, Larsen was through. Inside the building, he followed a long corridor to a room where Vice President Dick Cheney and members of the national-security staff soon joined him. Also in the room were Tara O'Toole, who is now the Obama administration's top official for biodefense research at the Department of Homeland Security, and Thomas Inglesby, who runs the Center for Biosecurity. Three months earlier, Larsen, O'Toole and Inglesby collaborated on a national-security exercise to simulate the effects of a smallpox attack. Now, with the twin towers in ashes, they had come to brief the vice president on their findings. As O'Toole began the presentation, Larsen studied Cheney's expression. The vice president showed no reaction as O'Toole listed the officials who participated in the simulation, the complications they encountered as they tried to develop an emergency response and the arguments that broke out as they watched the disease spread beyond control. She concluded by telling the vice president that the country was unprepared for a biological attack. Cheney nodded. "O.K.," he said. But what are we looking for? What does a biological weapon look like? At this, Larsen reached into his briefcase and pulled out a small test tube. "Mr. Vice President," he said, "it looks like this." Inside the tube was a weaponized powder of Bacillus globigii, almost genetically identical to anthrax. "And by the way," Larsen said, "I just smuggled this into your office." At one of the most secure buildings in the world, in a moment of unprecedented alarm, the White House guards had searched Larsen's briefcase - and never even saw the powder. "They were looking for the wrong things," Larsen says now. They still are. The specter of a biological attack is difficult for almost anyone to imagine. It makes of the most mundane object, death: a doorknob, a handshake, a breath can become poison. Like a nuclear bomb, the biological weapon threatens such a spectacle of horror - skin boiling with smallpox pustules, eyes blackened with anthrax lesions, the rotting bodies of bubonic plagues - that it can seem the province of fantasy or nightmare or, worse, political manipulation. Yet biological weapons are as old as war itself. The ancient Hittites marched victims of plague into the cities of their enemies; Herodotus described archers" firing arrows tipped with manure. By the 20th century, nearly every major nation developed, produced and in some cases used a panoply of biological weapons, including anthrax, plague, typhoid and glanders. A decade after the 9/11 attacks, it is easy to forget the anthrax letters that sprang up just a few weeks later and to dismiss the fear that swept the country as a relic of a fragile moment that already belongs to history. But in the wake of those events, many national-security experts began to reconsider the risk of a biological attack - and reached some unsettling conclusions. Since the collapse of the Soviet Union, most scientists had assumed that the difficulty of building a bioweapon was far beyond the ability of a terror cell, but looking again in the early 21st century, many experts came to believe that advances in laboratory technology brought the science within reach. "What took me three weeks in a sophisticated laboratory in a top-tier medical school 20 years ago, with millions of dollars in equipment, can essentially be done by a relatively unsophisticated technician," Brett Giroir, a former director at the Defense Advanced Research Projects Agency (Darpa), told me recently. A person at a graduate-school level has all the tools and technologies to implement a sophisticated program to create a bioweapon. Even some nuclear experts began to wonder if the risk of a biological attack had eclipsed the nuclear threat. Graham Allison, the founding dean of Harvard's John F. Kennedy School of Government and a leading expert on nuclear proliferation, told me: "Nuclear terrorism is a preventable catastrophe, and the reason it's preventable is because the material to make a nuclear bomb can't be made by terrorists. But in the bio case - oh, my God! Can I prevent terrorists from getting into their hands anthrax or other pathogens? No! Even our best efforts can't do that. I think the amazing thing is that one hasn't seen more bioterrorism, given the relative ease of making a bioweapon and the relative difficulty of defending.