We report an experimental demonstration of all-optical switching at ultralow light levels in coherently prepared Rb atoms. A signal light pulse is switched on and off by a control light pulse at different frequencies in a four-level atomic system based on multiphoton interferences. We observed a switching efficiency of 55% with the signal and control light pulses containing approximately 20 photons each, corresponding to a control energy density of approximately 10(-5) photons per atomic cross section lambda(2)/(2pi).