To achieve, an in vivo repair of injured mammalian nerve tissue, an effective amount of a biomembrane fusion agent is administered to the injured nerve tissue. The application of the biomembrane fusion agent may be performed by directly contacting the agent with the nerve tissue at the site of the injury. Alternatively, the biomembrane fusion agent is delivered to the site of the injury through the blood supply after administration of the biomembrane fusion agent to the patient. The administration is preferably by parenteral administration including intravascular, intramuscular, subcutaneous, or intraperitoneal injection of an effective quantity of the biomembrane fusion agent so that an effective amount is delivered to the site of the nerve tissue injury.