OBJECTIVE: To evaluate the healing after elevation of the sinus mucosa when a collagen membrane was placed between the sinus mucosa and a xenograft used as filler. MATERIALS AND METHODS: Eighteen rabbits were used. Sinus mucosa elevation was performed bilaterally, and a collagen membrane was applied subjacent to the sinus mucosa only at a randomly selected test site. At both sites, a collagenated corticocancellous porcine bone was placed within the elevated space and the access window was covered with a collagen membrane. The animals were sacrificed after 2, 4, and 8 weeks of healing, six animals for group. Ground sections were prepared. RESULTS: At the histomorphometric evaluation, the elevated area after 2 and 8 weeks was 11.8 and 8.8 mm(2) at the test, and 10.0 and 5.3 mm(2) at the control sites, respectively. The available area was obtained subtracting the remaining area occupied by the membrane from the elevated area and, after 8 weeks, was 6.7 +/- 0.9 mm(2) . After 8 weeks of healing, the mineralized new bone within the elevated space was 18.2 +/- 5.5% at the test and 26.7 +/- 7.7% at the control sites. Within the available space at the test site, the percentage was 27.3 +/- 7.0% after 8 weeks of healing. At 2 and 8 weeks of healing, within the elevated space, the xenograft proportion was 30.9 +/- 4.4% and 6.9 +/- 2.8% at the test, and 35.2 +/- 7.3% and 9.6 +/- 4.9% at the control sites, respectively. CONCLUSIONS: The placement of a collagen membrane subjacent the sinus mucosa did not reveal any major morphometric difference. The collagen membrane was not completely resorbed after 8 weeks.