Background: The purpose of this pilot study was to evaluate the healing potential and reosseointegration in ligature‐induced peri‐implantitis defects adjacent to various dental implant surfaces following lethal photosensitization.Methods: A total of 36 dental implants with 4 different surface coatings (9 commercially pure titanium surface [CPTi]; 9 titanium plasma‐sprayed [TPS]; 9 hydroxyapatite [HA]; and 9 acid‐etched [AE]) were inserted in 6 male mongrel dogs 3 months after extraction of mandibular premolars. After a 2‐month period of ligature‐induced peri‐implantitis and 12 months of natural peri‐implantitis progression, only 19 dental implants remained. The dogs underwent surgical debridement of the remaining dental implant sites and lethal photosensitization by combination of toluidine blue O (100 µg/ml) and irradiation with diode laser. All exposed dental implant surfaces and bone craters were meticulously cleaned by mechanical means, submitted to photodynamic therapy, and guided bone regeneration (GBR) using expanded polytetrafluoroethylene (ePTFE) membranes. Five months later, biopsies of the implant sites were dissected and prepared for ground sectioning and analysis.Results: The percentage of bone fill was HA: 48.28 ± 15.00; TPS: 39.54 ± 12.34; AE: 26.88 ± 22.16; and CPTi: 26.70 ± 16.50. The percentage of reosseointegration was TPS: 25.25 ± 11.96; CPTi: 24.91 ± 17.78; AE: 17.30 ± 15.41; and HA: 15.83 ± 9.64.Conclusion: These data suggest that lethal photosensitization may have potential in the treatment of peri‐implantitis. J Periodontol 2003;74:338‐345