Even as the Bush Administration makes its case for an attack on Iraq we are still trying to get humans inside the country to ferret out biological and chemical weapons, not to mention nuclear ones. But consider this scenario in the not-too-far future: Flying over suspected terrorist sites, unmanned vehicles stocked with microsensors sniff for evidence of bioweapons and analyze it on the spot. If not quite foolproof, a coming generation of biosensor technology promises to provide more accurate and timely monitoring, and perhaps even obviate the need for human inspection of suspected terrorist spots--and all the diplomatic and safety issues that entails. Indeed, given the ease of concocting bioweapons in the smallest of laboratories, our only protection from bioterrorism is early detection.

Seattle-based Research International is using a machine that is employed to detect toxins in agriculture, like deadly forms of E. coli, as a bioweapon sniffer. A complementary machine can test air samples converted into a liquid form. Weighing 12 pounds (a handheld version is also being studied), it has already been successfully deployed on an American-made unmanned aerial vehicle, says Elric Saaski, Research International's chief executive. The company is also working with British Aerospace to incorporate the device into antiterrorism tools.

The device uses the same antibody technology that medical labs use in testing for things like flu viruses. It contains antibodies stuck on the ends of tiny fiber-optic strands. The antibodies are programmed to latch onto different biowarfare agents captured from air samples. Then a second batch of antibodies is applied; this batch has tail ends that fluoresce after being exposed to light of a certain wavelength. The fluorescent antibodies will stick only if a target bacterium or other agent is present. When the sample is exposed to a pulse of laser light, photodetectors at the ends of the fiber-optic strands will identify the telltale fluorescence.

One weakness of biodetection systems like this is that they rely on organic molecules, which could degrade in the desert heat. San Diego-based biotech startup Biopraxis gets around that challenge with a prototype detector that uses Raman spectroscopy to optically fingerprint potential bioagents.

In yet another approach, machines search for snippets of DNA common to certain bioweapons, thus detecting minuscule quantities of pathogens leached into the air around a bioweapons factory. These DNA scanners can also be engineered to detect designer pathogens altered to be more deadly. Cepheid of Sunnyvale, Calif. delivered a first-generation DNA detection device to the U.S. military in January that scans for anthrax, plague, tularemia and botulism.

San Diego-based Nanogen is adapting its electronic DNA chips, currently used in medical diagnostics and pharmaceutical research, for use in a machine capable of performing real-time surveillance of dozens of different biowarfare pathogens. The system's reliance on electronics makes it fast, both for detection and reporting. Nanogen has already built a prototype the size of a laptop computer. The Nanogen chip detects DNA by using the tiny strands of DNA to complete circuits. If a piece of anthrax DNA is present, it will bind to two probes on the chip, completing a circuit so electricity will flow to mark its presence.

Mounting detection cartridges on unmanned aerial vehicles that can loiter over suspected bioweapons plants has obvious advantages. It's certainly safer than sending operatives into the Sudan to dig for soil samples around pharmaceutical plants. More likely, at the start, the microdevices will be carried by military personnel and left inside or near suspicious sites, where the sensors can provide continuous monitoring.

The political advantages are mighty, too. The U.S. could look for bioweapons whenever, wherever we wanted. No longer will our leaders be held hostage to half-baked inspection agreements with rogue nations. The only way to stop bioterrorism is through clandestine monitoring, exposure and retribution.