article about Nanotechnology on rationalwiki

[JohnnyYesterday]

Autonomous microbots might be difficult to program and control but attaching an external device to the patient's body, which injects tiny flexible tendrils into the body, which can then seek out the source of an ailment and fix it or be used for diagnostics, seems to make some of these problems a little simpler. The "command & control" - problem is outsourced to an external device of arbitrary size and complexity instead of trying to "cram" all this complexity into a tiny bot.

Potentially, they could be radio controlled.

Robert Freitas has done a huge amount of work analyzing medical micromachines. He's authored two technical books on the subject, so far. You don't have to buy them in dead-tree-version, by the way, they're free on his website.