Purpose: To determine whether sinus membrane elevation alone can lead to new bone formation on the maxillary sinus floor. Materials and Methods: Among patients who were to receive implant treatment, those who had 4 to 5 mm of bone height in the maxillary sinus floor (as measured radiographically) were selected as candidates for sinus membrane elevation. The lateral sinus wall was exposed through a buccal mucoperiosteal incision. The sinus membrane was elevated through a bone window, and the space underneath the membrane was filled with absorbable collagen sponge (Collaplug). In the presence of blood in the space, the collagen sponge was left to soak up the blood; in the deficiency of blood, the sponge was saturated with venous blood drawn from the brachial vein. The mucoperiosteal flap was repositioned and closed with interrupted silk sutures. The sinus was left to heal for 6 months. Core specimens of the maxillary sinus floor were obtained using a trephine bur at 6 months after sinus elevation in patients treated between January 2006 and June 2009. The trephined sites were used for implant placement. The biopsy specimens were analyzed histologically to identify the presence and amount of new bone tissue. Results: Thirteen specimens from eight patients were included in the study. Microscopically, 11 specimens exhibited no recognizable new bone tissue. Two specimens exhibited a small amount of woven bone on the surface of the sinus floor. Conclusion: Within the limits of this study of eight patients, little to no new bone formation was observed on the maxillary sinus floor at 6 months following sinus membrane elevation and support with blood-soaked collagen sponges. Keywords: bone formation, bone graft, lateral window, maxillary sinus, membrane elevation, sinus floor augmentation