In the gingival tissues of patients with periodontitis, inflammatory responses are mediated by a wide variety of genes. In this study, we screened for differentially expressed genes (DEGs) in periodontitis compared with normal tissue using an annealing control primer (ACP) system. By ACP RT-PCR analysis, we obtained about 160 amplicons, 8 of which were found to be differentially expressed. DEGs in patients with periodontitis were thus successfully and reliably identified by the ACP-based RT PCR technique. The DEGs identified in the screen may also enhance our understanding of the pathogenesis of periodontitis.