Periodontal diseases cause an inflammation and degradation of periodontal tissues and missing of teeth. The incidence rate of periodontal diseases is high in middle-aged and elderly people.A reasonable diagnosis of periodontal diseases is very important to keep teeth, however, conventional examinations of periodontal diseases is not necessarily exact and objective. Gingival crevicular fluid (GCF) is an exudate secreted from periodontal tissues and contains many components including proteolytic enzymes, inflammatory cytokines, blood-associated proteins, cellular and bacterial fragments. Because some proteins in GCF are related to inflammation, tissue degradation and bone metabolism, those proteins have been studying as a diagnostic marker of periodontal diseases. GCF is noninvasively collected using a sterile paper strip and biomarkers are determined using enzyme-linked immunosorbent assay (ELISA) and enzyme activity assay. We identified calprotectin, an inflammationrelated protein, in GCF and calprotectin level in GCF from periodontitis sites was significantly higher than that of healthy control. Calprotectin level in GCF was positively correlated to gingival index and other biomarkers and decreased by periodontal treatments. Resistin is an adipocytokine and its level increases in some inflammatory diseases. Resistin level in GCF from periodontitis sites was high compared to the level of healthy control samples. Procollagen type I C-terminal peptide (PICP) is a biomarker for bone metabolism and its level was high in GCF collected from periodontitis sites. These results suggested that calprotectin, resistin and PICP are useful biomarkers for periodontal diseases. On the other hand, we showed that glycated albumin (GA), a marker of diabetes mellitus (DM), was contained in GCF and GA level in GCF from DM patients was significantly higher than that of non-DM individuals. Components in GCF may be biomarkers of systemic diseases as well as periodontal diseases and their determination will be useful diagnostic examination of some diseases. Recently, we have been studying the determining system of GCF calprotectin, including microchip ELISA, surface plasmon resonance assay and immuno-chromatography assay. When GCF biomarkers are determined using the determining systems, we will simply, exactly and objectively diagnose periodontal diseases at our dental offices.