The amplitude of cochlear‐microphonic responses in cats was attenuated up to 18 dB during both induction and recovery from nitrous oxide anesthesia, with smaller changes (up to 3 dB) occurring during the periods of maintained anesthesia. This response variability was clearly related to alterations of middle‐ear pressure and could not be attributed to changes in middle‐ear muscle or efferent olivocochlear bundle activities. Middle‐ear pressure rose during inhalation of nitrous oxide with periodic abrupt returns to baseline levels during the period of maintained anesthesia; pressure became negative after withdrawal of nitrous oxide.