The influence of two fixation buffers on the quantitative cytoarchitecture of the cochlear spiral ganglion in guinea pigs was evaluated morphometrically. After fixation with phosphate buffered 1.3% OsO4 granular spiral ganglion cells lost 45% of their average individual volume as compared to the volume after fixation with s-collidine buffered 1.3% OsO4. Using the two fixatives there was no significant difference of the volume proportion of cell nuclei, mitochondria, lysosomes and rough endoplasmic reticulum per unit volume cytoplasm of the granular spiral ganglion cells. The volume proportion of their ribosomes and their Golgi apparatus per unit volume cytoplasm increased 3.5fold after fixation with phosphate buffered OsO4. The volume density of the granular ganglion cells decreased by 30%, the volume density of the interganglionar space (= space between granular ganglion cells) showed an increase of 50% using phosphate buffer. Mostly the extracellular space was participating in this relative increase of the interganglionar space. As a result fixation of the spiral ganglion for morphometric studies should be performed using s-collidine buffered OsO4. The morphometric findings underline the presumption of semicompact myelin being a fixation artefact.