Анотация: The present study aimed to determine the possibility of application of guided bone regeneration in experimental non-fixed ulnar defects in dogs. In 24 dogs, a total of 48 ulnar bone defects were created (24 left and 24 right). The dogs were allotted to 4 groups (6 animals each). The right defects were treated as followed: group I - the bone defects were filled with autocancellous bone; in group II - with allocancellous bone; in group III - with xenocancellous bone and in group IV - with xenocancellous bone and bioceramics. The defects of left ulnas were treated similarly and isolated from adjacent soft tissues with enzymatically processed and freeze-dried canine dura mater. Both ends of the ulna were not fixed by osteosynthesis. In the post operative period, radiological and clinical surveys were performed immediately after the surgery and 1, 2, 4 and 6 months after treatments. The guided bone regeneration using processed dura mater slowed down the osteogenesis in segmental non-fixed canine ulnar defects regardless of the type of used osteoinductor graft