Morphological and radiological methods were used to study regeneration of the damaged bone of rat mandibles after application of platelet-enriched fibrin clot. A bone hole was artificially created, and in the natural course of regeneration, the hole was immediately filled with blood and there a blood clot formed. After one week of healing, separate islands of young bone tissue appeared. After two to three weeks, the opening in the mandible was completely replaced by the young bone tissue. When a similar bone hole was filled with autological fibrin clot, the blood clot did not form. But after one week the entire hole was filed with newly-formed fused bone tissue. By the second week after the use of fibrin clot, the bone hole had further healed and bone callus was formed.