Auditory nerve fibers can be categorized by their spontaneous discharge rates (SRs). Although the significance of these categories is not known, it has been suggested that the low and medium SR fibers may contribute to frequency analysis at signal levels at which the more sensitive high SR fibers are saturated. Data obtained from chinchilla auditory nerve fibers in response to two‐tone stimuli are consistent with that possibility. The stimuli were presented in a tone‐on‐tone masking paradigm analogous to that used by Long and Miller [Hear. Res.4,279–285 (1981)] for psychophysical measurements in chinchillas, and average discharge rate data from fibers with medium and high SRs were analyzed separately. Good agreement between the “masked thresholds” of medium SR fibers and the behavioral masked thresholds was observed. Masked thresholds of medium SR fibers were sometimes lower than the masked thresholds of high SR fibers, even though their quiet thresholds tend to be higher. This difference was greatest (10–15 dB) for masker‐probe tone pairs with the smallest frequency separations. High SR fibers were often driven to saturation by the masker, so that no masked threshold could be estimated; however, probe tones nearly always produced rate changes in medium SR fibers. [Supported by NIH.]