The purpose of this study was to histomorphometrically evaluate the percentage of vital bone after grafting of maxillary sinuses using two different concentrations of recombinant human bone morphogenetic protein/acellular collagen sponge (rhBMP-2/ACS) combined with mineralized cancellous bone allograft (MCBA) and to compare the results to a control sinus grafted with MCBA only. Thirty-six sinuses in 18 patients had two of three of the graft combinations including: (1) control, MCBA only; (2) test one, MCBA + 5.6 mL of rhBMP-2/ACS (containing 8.4 mg of rhBMP-2); or (3) test two, MCBA + 2.8 mL of rhBMP-2/ACS (containing 4.2 mg of rhBMP-2). Histologic cores were taken 6 to 9 month following sinus augmentation. The results showed no statistically significant differences in vital bone between the two test groups compared to the control sinus group treated with MCBA alone. Future studies involving more cases and evaluating survival of implants placed in these augmented sinuses are needed to verify the results of this randomized prospective study.