Multiagent control provides strategies for aggregating microscopic robots (“nanorobots”) in fluid environments relevant for medical applications. Unlike larger robots, viscous forces and Brownian motion dominate the behavior. Examples range from modified microorganisms (programmable bacteria) to future robots using ongoing developments in molecular computation, sensors and motors. We evaluate controls for locating a cell-sized area emitting a chemical into a moving fluid with parameters corresponding to chemicals released in response to injury or infection in small blood vessels. These control methods are passive Brownian motion, following the chemical concentration gradient, and cooperative behaviors in which some robots use acoustic signals to guide others to the chemical source. Control performance is evaluated using diffusion equations to describe the robot motions and control state transitions. The quantitative results show these control techniques are feasible approaches ...