Nanotechnology researchers are sick of hearing about ‘grey goo’. Their research is still largely speculative, yet the notion that swarms of tiny self-replicating robots could escape from laboratories and destroy our world comes up time and time again when nanotechnology is discussed with the public.

But researchers can take heart: the author who arguably did most to stir up the fears in the first place has publicly dismissed the scare stories. He says he wishes he had never coined the term ‘grey goo’, which is used to encapsulate them.

In his 1986 book Engines of Creation, Eric Drexler speculated that self-replicating robots with molecular-scale dimensions could be used to build everyday goods cheaply and efficiently. He also noted that such ‘nanobots’ could be dangerous if they escaped: “We cannot afford certain kinds of accidents.”

The idea gained a lot of influence, and the term ‘grey goo’ appears regularly in popular accounts of nanotechnology. It was also the inspiration for Prey, a bestselling 2002 novel by Michael Crichton that is being made into a film.

But in a commentary published on 9 June (see C. Phoenix & E. Drexler Nanotechnology 15, 869–872; 2004), Drexler acknowledges that nanoscale manufacturing does not require self-replicating devices. “I wish I had never used the term ‘grey goo’,” he told Nature.

Drexler says that if he could write Engines of Creation again, he would barely mention self-replicating nanobots. Instead, he would focus on the possibility that nanoscale manufacturing will become a miniature version of conventional processes, in which a single device moves along a conveyor belt and is built up in a series of discrete operations.

The California-based author says he has gone public now because of worries about the way nanotechnology is being perceived. “Fears associated with that old scenario are interfering with current research,” says Drexler. “Researchers resent it and I want to clean up the mess.”

But Drexler's repentance may not change much. Experts who track public attitudes to nanotechnology say that some environmental groups have played on fears about ‘grey goo’ to publicize their more genuine concerns about who will benefit from the technology. “If the term wasn't here, the groups would come up with another phrase,” says one expert.