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Cochlear microphonics were recorded from round-window electrodes in ten cats. The ears were stimulated alternately with broad-band noise and with pure tones in the frequency range 200 to 8000 Hz. The sound-pressure level (SPL) of the pure tone was matched in intensity to the SPL of the same frequency component within the noise, after correcting to a one-cycle bandwidth. Results showed that the cochlear input-output curve with noise was generally similar in shape to that produced by pure tones. However, noise was seen to suppress microphonic output at all frequencies tested. The tone-noise response ratio was both frequency- and intensity-related. Suppression of the noise response was greater with increasing stimulus intensity. Suppression was greater at frequencies above 800 Hz and was broadly related to cochlear sensitivity. Overload occurred at lower SPL's with noise stimulation than with pure-tone stimulation. [Research supported by grants from the National Institutes of Neurological Diseases and Blindness and an anonymous donation to the Division of Otolaryngology.]