Any advanced research carries inherent risks, but nanotechnology bears a special burden. The field's bid for respectability is coloured by the association of the word with a cabal of futurist who foresee nano as a pathway to a techno-utopia: unparalleled prosperity, pollution-free industry, even something resembling eternal life. In 1986-five years after IBM researchers Gerd Binnig and Heinrich Rohrer invented the scanning tunnelling microscope, which garnered them the Nobel Prize-the book Engines of Creation, by K. Eric Drexler, created a sensation for its depiction of godlike control over matter. The book describes self-replicating nanomachines that could produce virtually any material good, while reversing global warming, curing disease and dramatically extending life spans. Scientists with tenured faculty positions and NSF grants ridiculed these visions, noting that their fundamental improbability made them an absurd projection of what the future holds. But the visionary scent that has surrounded nanotechnology ever since may provide some unforeseen benefits. To many non-scientists, Drexler's projections for nanotechnology straddled the border between science and fiction in a compelling way. Talk of cell-repair machines that would eliminate aging as we know it and of home food-growing machines that could produce victuals without killing anything helped to create a fascination with the small that genuine scientists, consciously or not, would later use to draw attention to their work on more mundane but eminently more real projects. Certainly, labelling a research proposal "nanotechnology" has a more alluring ring than calling it "applied mesoscale materials science." Less directly, Drexler's work may actually draw people into science. His imaginings have inspired a rich vein of science-fiction literature. As a subgenre of science fiction-rather than a literal prediction of the future-books about Drexler Ian nanotechnology may serve the same function as Star Trek does in stimulating a teenager's interest in space, a passion that sometimes leads to a career in aeronautics or astrophysics. The danger comes when intelligent people take Drexler's predictions at face value. Drexler Ian nanotechnology drew renewed publicity last year when a morose Bill Joy, the chief scientist of Sun Microsystems, worried in the magazine Wired about the implications of nanorobots that could multiply uncontrollably. A spreading mass of self-replicating robots-what Drexler has labelled "Gray goo"- could pose enough of a threat to society, he mused, that we should consider stopping development of nanotechnology. But that suggestion diverts attention from the real nano goo: chemical and biological weapons.