This is a well-designed study that evaluates the use of a barrier membrane in critical-size defects in the maxilla of rabbits. The investigation compares bone healing in maxillary osteotomies with and without the use of a resorbable collagen membrane and compares bone plate osteosynthesis, wire osteosynthesis, and no fixation. The results are what one would logically expect given these parameters. The bone healing was greater in those defects with more rigid fixation and those defects protected by a barrier membrane showed more osseous fill than the unprotected defects. The investigators have provided an excellent description of the exclusive role of the barrier membrane in bone wound healing. Other roles of the barrier membrane that should be considered include a combination of mechanical, cellular, and molecular mechanisms such as prevention of fibroblast mass actions, prevention of contact inhibition by heterotopic cell interaction, exclusion of cell-derived soluble inhibitory factors, local concentration of growth stimulatory factors, and the stimulatory properties of the membrane itself. 1 Dahlin C Scientific background of guided bone regeneration. in: Implant Dentistry. Quintessence, Chicago, IL1994: 31-48 Google Scholar Another important role for the barrier membrane is space-making to prevent the collapse of overlying tissue into the defect. Space-making is more difficult with resorbable collagen membranes than with nonresorbable expanded-polytetrafluoroethylene, both reinforced and nonreinforced. The use of barrier membranes to enhance osseous healing has been well established but is very technique-sensitive and requires attention to the placement of the barrier, stabilization, and the soft tissue closure over the barrier. Too frequently surgeons have equated the use of the membrane itself with the principle of guided tissue regeneration, thus ignoring the basic steps necessary to achieve success.