Abstract: A method and apparatus for controlling rodents is disclosed utilizing ultrasonic signals. The ultrasonic signals are of the square wave type. They are varied from approximately 28 to 20 KHz during the first time period of approximately 20 microseconds, then maintained at a frequency of approximately 20 KHz for a second time period of approximately 780 microseconds. The generated square wave signals are converted to sound waves by a transducer such as a speaker. The frequencies employed and the duration of these frequencies are selected to maximize the irritating effect upon the rodents.