Introduction: In addition to bacteria, viruses have been reportedly implicated in periodontitis. However, the available data are confined to Toll-like receptor 2 (TLR2) and TLR4, which recognize bacterial products in periodontitis. In the present study, we investigated the expression levels of TLR5, -7, and -9 messenger RNAs (mRNAs) in addition to those of TLR2 and -4, and compared gingivitis and periodontitis. Interferon-α1 (IFN-α1), which is important for the antiviral response, was also compared. Methods: Gene expression was analyzed using quantitative real-time polymerase chain reaction for 59 periodontitis and 27 gingivitis tissue samples together with viral serology in some patients. The presence of plasmacytoid dendritic cells (pDCs), a robust producer of IFN-α, was immunohistochemically analyzed in an additional seven periodontitis and two gingivitis specimens. Results: The expression levels of TLR2, -4, -7, and -9 were significantly higher in periodontitis lesions than gingivitis lesions. The expression level of TLR5 was comparable to levels of TLR2 and -4; however, no significant difference was found between gingivitis and periodontitis. Although the expression of IFN-α1 mRNA was higher in periodontitis lesions compared with gingivitis lesions, the level was quite low. Only a few pDCs were found in some periodontitis specimens. No difference was found for antibody-positivity between gingivitis and periodontitis. Conclusion: This is the first study to show that a variety of TLRs are up-regulated in periodontitis lesions compared with gingivitis lesions, suggesting that diverse microbial and possibly viral antigens are involved in the pathogenic mechanisms for periodontal diseases. However, the ligands recognized by the various TLRs in periodontal lesions remain to be determined. © 2007 The Authors.