We report the integration of a complex biological system and a nanoelectronic device, demonstrating that both components retain their functionality while interacting with each other. As the biological system, we use the cell membrane of Halobacterium salinarum. As the nanoelectronic device, we use a nanotube network transistor, which incorporates many individual nanotubes in such a way that entire patches of cell membrane are contacted by nanotubes. We demonstrate that the biophysical properties of the membrane are preserved, that the nanoelectronic devices still function as transistors, and that the two systems interact. Further, we use the interaction to study the charge distribution in the biological system, finding that the electric dipole of the membrane protein bacteriorhodopsin is located 2/3 of the way from the extracellular to the cytoplasmic side.Nanobioelectronics, the integration of biological processes and molecules with nanoscale fabricated structures, offers the potential for electronic control and sensing of biological systems. 1 As a specific example, carbon nanotubes have been suggested for use as prosthetic nervous implants in organs such as eyes and ears. 2 To achieve this goal requires the parallel preparation 3 of fully functional biological systems and nanoelectronic systems that are integrated together. One major obstacle is the preservation of functionality in both systems. For example, while biological systems ranging from lipids 7 to living cells 2 have been assembled on nanotube substrates, the nanotubes have served only as mechanical supports, without electronic functionality. A second major obstacle is the difference in scale between nanostructures and biological systems. While nanotubes are comparable in size to individual proteins, they are much smaller than cells. Thus, nanotube electronic devices have been used as singlemolecule sensors 5a,7a rather than to communicate with complex biological systems. Here, we achieve integration between a functioning nanotube transistor and a cell membrane. We use nanotube networks, a recently developed class of nanotube devices, to bridge the gap in size between nanotechnology and biotechnology. To demonstrate the power of the approach, we use the nanobioelectronic devices to extract information about the charge distribution in the particular membrane used, thereby contributing to the resolution of a long-standing question about charge distributions within that membrane. 6