To investigate which fixative is most suitable for the preservation of cochlear hair cells three main groups of fixatives were used: 1. 3% glutar aldehyde in various buffers (osmolality altered). 2. Glutar aldehyde/paraform aldehyde combination (ad modum Karnovsky). 3. Osmic acid solutions (OsO4) in veronal acetate buffer according to Rhodin (1954). The 2% osmic acid fixative (350--370mosm/kg) resulted in an excellent ultrastructural preservation; an acceptable result was obtained with a 3% glutar aldehyde fixative in 0.1 M sodium phosphate buffer, 600--700 mosm/kg and the Karnovsky's fixative.