Purpose: Nitrite is a stable end-product of nitric oxide oxidation. The aim of the present study was to quantitatively analyze peri-implant sulcular fluid (PISF) nitrite levels in a longitudinal study design to evaluate the potential changes in nitric oxide metabolism in relation to the clinical status of the peri-implant site and the loading style of the dental implants. Materials and Methods: A total of 34 implants, either early loaded (EL) or delayed loaded (DL), in 17 patients were followed up for a period of 18 months. Clinical parameters were recorded, PISF samples were obtained, and PISF nitrite levels were spectrophotometrically determined. Clinical measurements and nitrite analysis were repeated at 1, 3, 6, 9, 12, and 18 months. Results: Despite the gradual decrease in clinical parameters, fluctuations in PISF total nitrite levels were observed during follow-up. The pattern of nitric oxide metabolism, as reflected by PISF nitrite levels, also demonstrated differences between EL and DL implants that diminished toward the end of the experimental period. Discussion: Although the presence of clinical and subclinical gingival inflammation contributes to the PISF total nitrite levels, nitric oxide metabolism is also associated with healing and bone remodeling, and the pattern of loading seemed to have an impact on nitric oxide production at dental implant sites. Conclusion: Nitric oxide production at dental implant sites seems to be tightly regulated to enable the maintenance of peri-implant bone. Keywords: comparative studies, dental implants, loading, longitudinal study, nitric oxide, nitrite