Aim of this study was to evaluate peri-implant tissue reactions to immediately loaded titanium plasma-sprayed implants in Macaca fascicularis monkeys. A total of 48 titanium plasma-sprayed implants were inserted (24 in the posterior maxilla and 24 in the posterior mandible). A metal superstructure was cemented 3 days after implant insertion on 24 implants (12 in the maxilla and 12 in the mandible) (test implants). The remaining 24 implants (12 in the maxilla and 12 in the mandible) were left unloaded (control implants). Nine months after implant placement a block section was carried out, the defect filled with non-resorbable hydroxyapatite, and all 48 implants retrieved. The implants were treated to obtain thin ground sections. Three slides were cut for each implant and examined under normal and polarized light and a morphometrical analysis done. All implants were covered by bone under light microscopy. The histomorphometrical analysis demonstrated that in test implants, the bone-implant contact percentage was 67.3% (± 7.6%) in the maxilla, and 73.2% (± 5.9%) in the mandible; in control implants the percentages were, respectively, 54.5% (± 3.3%) and 55.8% (± 6.5%). In the test implants the bone around the implants tended to have a more compact appearance. In conclusion, our study demonstrated that in test implants the bone-implant contact percentage was significantly greater than in the controls (P < 0.01) and no fibrous connective tissue was present at the interface. J Periodontol 1998;69:321–327.