Collagen degradation products of the carboxyterminal region possibly reflect bone and attachment loss. In the present study, the Serum CrossLaps One-Step enzyme-linked immunosorbent assay was used to determine a specific part of the carboxyterminal region of type I collagen, the CrossLaps. Samples of peri-implant and gingival crevicular fluid of 111 implants and 53 teeth from 47 partially or completely edentulous patients were examined in reference to levels of CrossLaps and b-glucuronidase (ßG), an established marker of periodontal disease. Clinical probing pocket depth (PPD), bleeding on probing (BOP), plaque accumulation, mobility, radiographic bone loss, and the occurrence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia were assessed. The mean values were: for PPD at implants 3.76 ± 1.41 mm, at teeth 3.44 ± 0.88 mm; for ßG at implants 0.364 ± 0.392 pU/min, at teeth 0.314 ± 0.209 pU/min; for CrossLaps at implants 0.069 ± 0.059 pmol/min, at teeth 0.082 ± 0.053 pmol/min. Bleeding on probing was significantly higher on implants than on teeth (McNemar test, P = .004). No significant difference of ßG levels was found between teeth and implants (Wilcoxon test). A negative correlation was found between ßG levels and CrossLaps levels at teeth (Pearson-rank correlation, P = .002). On implants, no significant correlation of these 2 parameters was seen, but significant correlations were found between sulcus fluid flow rate and PPD (P = .012), bG levels and bone loss (P 0.0005), and CrossLaps levels and PPD (P = .011). CrossLaps can be detected in both gingival and peri-implant crevicular fluid. While rising levels of ßG may indicate acute peri-implantitis, CrossLaps may not, but could play a role as a marker of ongoing attachment loss.