In the course of experiments involving the response of single auditory nerve‐fibers, it was found that watch ticks elicit synchronized potentials which can be recorded from a great number of fibers. An almost identical response is easily obtained from the round window. Both can be suppressed by pure tones, a frequency around 4050 c.p.s. being most effective for a particular watch. There is experimental evidence that the tick‐response, also if recorded from the fenestra rotunda, consists almost entirely of nerve potentials (aural microphonics being negligibly small in this case). Thus, it is possible to record a practically pure nerve‐response from the cochlea. This opportunity was used to determine the locus of suppression of the click‐potential by the masking pure tone. It is found that damage to the auditory nerve does not abolish the masking effect. One would therefore conclude that it takes place within the cochlea. This is in agreement with an assumption made by Galambos in his report on suppression of a single nerve‐fiber response by a second pure tone.