Spike discharges from single fibers in the auditory nerve of anesthetized cats were recorded with micro‐electrodes. Rates of discharge were measured as functions of the frequencies and levels of either single tone bursts or of the sum of two simultaneous tone bursts. From these data, a mathematical expression relating rate of discharge to parameters of a two‐tone stimulus is derived. The rate of response is written as the sum of a “spontaneous” part and a driven part. The driven part of the response to two tones is a weighted sum of the driven parts of the responses to the individual tones presented alone. The weighting factors to a first approximation depend only on the ratio of the levels of the two tones and on their frequencies. The relationship of this stimulus response formulation to existing data and to auditory system models is discussed.