Purpose: The aim of the present study was to analyze the 2 molecular measures of inflammation: (1) the nitrite, an end metabolite of nitric oxide (NO) oxidation and (2) myeloperoxidase (MPO). Both are found in peri-implant sulcus fluid (PISF) of implants and gingival crevicular fluid (GCF) of natural teeth in healthy or diseased states. Materials and Methods: A total of 109 tooth or dental implant sites, either healthy/noninflamed, inflamed (Gingival Index [GI] > 0), or affected by periodontitis, were classified, and GCF/PISF samples were obtained. GCF/PISF MPO and nitrite levels were spectrophotometrically determined. For comparison of clinical parameters and PISF/GCF nitrite and MPO levels, Kruskal-Wallis analysis followed by Mann-Whitney test with Bonferroni correction was performed. Healthy/noninflamed, slightly inflamed, moderate/severely inflamed sites were also analyzed using the Kruskal-Wallis test followed by the Mann-Whitney test with Bonferroni correction. The correlation between nitrite and MPO levels and clinical inflammatory status were analyzed with Spearman's correlation coefficient. Results: Clinical parameters, including both the GCF and PISF volumes, demonstrated gradual increases with the presence of gingival/peri-implant inflammation (P .05). Despite the higher PISF than GCF volume at healthy sites (P = .001), there were no volumetric differences at inflamed sites (P = .771). PISF from inflamed sites (P = .025) and GCF from gingivitis and periodontitis sites presented higher total MPO levels (P .05) than samples from noninflamed sites. Despite the relatively stable GCF nitrite levels at healthy and diseased sites, PISF from inflamed sites had higher nitrite content than noninflamed sites (P .05). Conclusions: The present study demonstrated the volumetric similarities of PISF and GCF in terms of response to inflammation. However, some differences between the 2 biochemical measures of inflammation and their presence in PISF and GCF were also observed. PISF is likely to have a considerable diagnostic potential for reflecting the biologic changes around load-bearing endosseous dental implants. (Cohort Study) (More than 50 references.) Keywords: dental implants, inflammation, myeloperoxidase, natural teeth, nitric oxide