CM‐responses were recorded in cats for seven frequencies between 150 cps and 7500 cps by means of differential electrodes in the basal cochlear turn. Both air‐ and bone‐conducted signals were used. The cochlear windows were closed by means of dental cement (the round‐window membrane being protected by silicone grease). A good seal was assured by (a) careful removal of the muco‐periost under microscopic control and (b) by anchoring the cement plug against the walls of the bulla or middle‐ear, respectively. Closure of either window resulted in a drop of BC responses of approximately 10–15 db. Additional closure of the other window had no noticeable effect unless the cochlear aqueduct had also been sealed off. In that latter case, additional response losses of approximately 5–8 db were observed. In no instance was it possible to abolish the response to BC sounds to the same degree (50–60 db) as was accomplished with respect to AC sounds by closure of the oval window alone.