Purpose: To investigate the effects of resorbable membrane on new bone formation in human maxillary sinus graft using anorganic bovine bone material histomorphometrically in a split-mouth study design. Materials and Methods: This prospective pilot study included six patients who required bilateral sinus augmentations prior to implant treatment. Each patient was grafted with anorganic bovine bone (Bio-Oss). The experimental side was covered with resorbable membrane (Bio-Gide) over the grafted sinus, and the control side was left uncovered. After 8 months of healing (range, 7 to 9 months), implants were placed. Biopsy samples were obtained from each side through the previously grafted sinus window and evaluated. Statistical analysis was performed using the Mann-Whitney U test at a significance level of alpha = .05. Results: The control side appeared to have a significantly greater amount of soft tissue than the experimental side (P = .026), whereas no significant differences in the amount of new bone were observed (P = .937). Conclusion: Resorbable membranes significantly reduced the amount of soft tissue formed in the sinus grafted with anorganic bovine bone material but had no effect on new bone formation. Schlagwörter: anorganic bovine bone, biopsy, histomorphometry, maxillary sinus