The aim of the present study was to evaluate the effect of bovine bone mineral placement as an adjunct to a guided bone regeneration (GBR)-barrier in experimental bone augmentation. Some 18 Sprague-Dawley rats underwent flap surgery in which non-permeable silicone domes were placed on the calvaria. A test group of 9 animals received domes filled with cancellous deproteinized bovine bone mineral (Bio-Oss). The domes of 9 control animals were left empty. The experiment was terminated after 8 weeks of healing. Inspection after histologic preparation found no signs of any foreign body reaction to the implanted bovine bone mineral, which seemed to be well integrated with the augmented tissue. The control specimens healed uniformly with new bone inside the domes at the base of the calvaria. The tissue inside the domes of the test specimens had a completely different architecture with new bone both at the base of the calvaria and at a distance from the base, surrounded by and in close contact with non-mineralized tissue and remaining bovine bone mineral. Some ingrowth of soft connective tissue, most likely from the sagittal skull suture could be seen in most test and control specimens. Histomorphometric analysis revealed that the total amount of augmented tissue was significantly greater in the test group (x = 1.93 +/- 0.21 mm2) than in the control group (x = 0.99 +/- 0.22 mm2), P < 0.001). The control domes contained 0.73 +/- 0.28 mm2 augmented bone, while the corresponding value for the test specimens was 0.35 +/- 0.13 mm2, significantly less than the controls (P < 0.01). The test domes contained 0.83 +/- 0.15 mm2 newly-formed non-mineralized calvarial tissue, significantly more than the controls (x = 0.26 +/- 0.16 mm2), P < 0.001). Remaining particles of bovine bone mineral constituted 0.76 +/- 0.14 mm2, or 39%, of the total amount of augmented tissue in the test group. A considerable shrinkage to about 69% of the height of the initial fill of bovine bone mineral at surgery appeared in the test domes after 8 weeks of healing. The reason for this was probably more due to a denser packing of the bovine bone mineral during healing than to resorptive activity. It was concluded that implantation of bovine bone mineral combined with GBR technique significantly enhances augmentation of calvarial tissue. Early mineralization, however, seems to be retarded compared to non-filled control specimens. Further studies should be made to determine the long-term maturation of augmented tissue including resorption pattern of the bovine bone mineral.