One of my favorite movies when I was growing up was Fantastic Voyage, where five people (one of whom was Racquel Welch) and their submarine-type vessel were shrunk down so they could be injected into the bloodstream of a scientist with the mission to dissolve a life-threatening blood clot.
Slow-Forward to 2008. Scientists at École Polytechnique de Montréal--the Polytechnical School of Montreal-- have developed something that may even be cooler than shrinking Racquel Welch.
By attaching little microscopic beads onto the bodies of magnetic, swimming bacteria, they have created little self-powered bacteria-robot hybrids that can be steered through the bloodstream by using the magnetic fields of an MRI.
By lacing the microbeads with anti-tumor agents, or perhaps clot-busting drugs, these little guys could be steered directly to their destination where they would leave their medical payloads.
Researchers are still working on techniques for removing them from the body post-procedure, as well as making sure that they don't get attacked by the body prior to finishing their mission.
In Fantastic Voyage, it was the body's defenses that ultimately destroyed the ship. Maybe these bots are destined to give their lives up for the greater good...