Purpose: The use of a limited number of implants for support of a removable partial denture (RPD) changes a Kennedy Class I or II situation to that of a Class III. This in vivo pilot study evaluated implant-supported distal-extension removable partial dentures (RPD) in 5 partially edentulous patients. Materials and Methods: Two implants (Branemark TU MK III, Nobel Biocare) were placed in a mandibular Kennedy Class I arch. To fabricate an implant-supported RPD (ISRPD), a conventional RPD base was fitted to the healing abutment with autopolymerizing acrylic resin (Uni-fast II, GC) to support the posterior aspect of the RPD. By changing the healing abutment to a healing cap, there was no connection between the denture base and implant, and the ISRPD became a conventional RPD (CRPD). Using a crossover study design, the masticatory movements (mandibular movements during mastication) of both dentures were measured using a commercially available tracking device (BioPACK, Bioresearch, Japan). The occlusal force and contact area were also measured using pressure-sensitive sheets and an image scanner (T-scan system). Using a visual analog scale (VAS), the 4 criteria of comfort, chewing,, retention, and stability were evaluated. All the data obtained were analyzed using Wilcoxen signed rank tests (alpha = .05). Results: There were no significant differences (P > .05) in masticatory movements between the ISRPD and the CRPD (5 patients: 4 women, 1 man). However, the ISRPD had significantly greater force and greater area than the CRPD (P = .043). The center of occlusal force of the ISRPD tended to move more distally compared to the CRPD. All the patients preferred the ISRPD for comfort, chewing, retention, and stability. Conclusions: One implant per edentulous area and a simple attachment technique yielded a stable distal extension RPD. INT J ORAL MAXILLOFAC IMPLANTS 2008;23: 1095-1101