A series of experiments was performed to study the effects of NaCl crystals on cochlear microphonics(CM) after application of it to round window membrane of ten guinea pigs. Also effects of Ringer's solution was studied for control group on five guinea pigs. The stimulating tone was 1 KHz continuous pure tone of 90 dB intensity. CM were recorded from round window membrane with single electrode technique during 60 minutes at every 5 minutes. The results were as follows : 1) CM showed an initial overshoot, which showed 6.6% increase of original level. The peak of overshoot was noted 2 minutes after NaCl crystal application. 2) The overshoot was followed by primary rapid decrease. The output of the bottom of decrease was noted 15 minutes after NaCl crystal application, and showed 43.6% of original level. 3) After then, CM showed incomplete temporary recovery, which showed 65.2% of original level until 45 minutes after NaCl crystal application. 4) Then, second decrease of more moderate rate was noted. At 60 minutes, CM showed 58.2% of original level. 5) After application of Ringer's solution, CM showed initial rapid decrease. But after removal it, CM showed continuous recovery up to 87.4% of original level at 60 minutes after application.