OBJECTIVE: Otitis media is one of the most common infectious diseases, especially in young children. Multiple factors affect the onset or development of otitis media. Human toll-like receptors recognize associated patterns and play a critical role in innate immune mechanisms. Toll-like receptors are considered to be important factors for clearance of infection and resolution of inflammation in otitis media. The purpose of this study was to evaluate the histological expression of toll-like receptor 2, which recognizes many kinds of pathogen-associated molecular patterns, and toll-like receptor 4, which recognizes lipopolysaccharide on Gram-negative bacteria, in tissue samples from patients with chronic otitis media and middle ear cholesteatoma. METHODS: Human middle ear tissue samples from 12 patients with chronic otitis media (n=7) and acquired middle ear cholesteatoma (n=5) were examined. Normal control middle ear samples without any inflammation were also included (n=7). The expressions of toll-like receptors 2 and 4 in middle ear tissues were examined immunohistochemically. RESULTS: Only one normal control middle ear sample showed weak expression of toll-like receptor 2, and toll-like receptor 4 was not observed in all control samples. On the other hand, both toll-like receptors 2 and 4 were markedly expressed in chronic otitis media and cholesteatoma. There was a significant difference between chronic otitis media and normal controls in the expressions of both toll-like receptors. Significant up-regulation of toll-like receptors 2 and 4 was observed in cholesteatoma as compared with control samples. CONCLUSIONS: Toll-like receptors 2 and 4 were strongly expressed in chronic otitis media and middle ear cholesteatoma. These findings suggest that toll-like receptors may play a principal role in human chronic otitis media and cholesteatoma.