In a technological advance that brings man and machine closer to each other, Zhong Lin Wang and colleagues at the Georgia Institute of Technology have built a nanogenerator that uses supersonic vibrations in blood to generate electricity. The power density of the generators approaches 4 W/cubic centimeter, which, if they could be made more cheaply, would open up a variety of applications, including biosensors and prosthetic implants. Running a scaled-down operating system like TinyOS, nanogenerator-powered bloodborne nanomachines will one day transform medicine, healing ailments without the need for surgery.