Objective: We present histopathological analysis of the temporal bones and up-to-date method by which messenger RNA (mRNA) manifestation can be analyzed.Methodology: Temporal bones from patients with sudden deafness and MELAS(mitochondrial encephalopathy, lactic acidosis and stroke-like episodes) were harvested at autopsy, and then fixed in 10％ neutral buffered formaldehyde, embedded in celloidin and cut into 20 micron thick sections.Their histopathological findings were analyzed.Three human temporal bones obtained at brain autopsy were fixed by formalin, decalcified by EDTA, and embedded in paraffin.The samples were isolated into spiral ligament, outer hair cells, spiral ganglion cells, and stria vascularis by laser microdissection.RNA was extracted.To identify the sites where COCH and SLC26A5 mRNA were expressed, semi-nested RT-PCR was performed.We also examined how long COCH mRNA could be amplified by semi-nested RT-PCR.