A device that produces electricity from blood could be used to turn people into "human batteries".
Researchers in Japan are developing a method of drawing power from blood glucose, mimicking the way the body generates energy from food.
Theoretically, it could allow a person to pump out 100 watts - enough to illuminate a light bulb.
But that would entail converting all the food eaten by the individual into electricity. In practice, less power would be generated since food is needed by the body.
However the scientists say the "bio-nano" generator could be used to run devices embedded in the body, or sugar-fed robots.
The team at electronics giant Panasonic's Nanotechnology Research Laboratory near Kyoto has so far only managed to produce very low power levels.
But the scientists ultimately expect to gain much greater performance from the device.
The battery is based on an enzyme capable of stripping glucose of its electrons, The Engineer magazine reported.
Dr Kazuo Eda, heading the research, said: "It is like the metabolism of food. Human bodies can process glucose and obtain energy. When glucose is oxidised, electrons can be obtained."
He believed bio-nano fuel cells were the next step for researchers after generators powered by hydrogen, natural gas and methanol now being developed for the car and energy industries.
PA