Cases involving two patients who presented post-traumatic prolonged disturbance of consciousness (PTPDC), namely akinetic mutism, and recovered from it after treatment with trihexyphenidyl were reported. Case 1: A seventy-one-year-old farmer. Five months after head injury, when he was first admitted to us, he was stable with signs of oligokinesia, katatonic posture, speechlessness, rigid muscle tones and positive cog-wheel phenomenon. One week after administration of the drug, his speech and voluntary movement improved remarkably. Two months after the treatment, he was able to walk, and was discharged from the hospital. Case 2: A forty-six-year-old man sustained major head trauma. In the acute stage, he was comatose with decerebrate posture. On the 15th hospital day, he showed a state of akinetic mutism with normal sleep - wakefulness cycle. Evacuation of the collected subdural fluid was done one month after the injury, which resulted in no change in his clinical state. Five months after the injury, trihexyphenidyl treatment was begun. A few days after the treatment, his motor activity and his facial expression obviously improved. One week after, he mimicked the word 'o-ha-yo (good morning)' after the physician's greeting. CT scan and magnetic resonance imaging in the chronic state of these patients showed bifrontal cerebral white matter lesions, which indicated old cerebral contusion. No brain stem lesions were detected with these examinations. Our two cases clearly did not belong to the category of post-traumatic parkinsonism because of their clinical courses, and their features shown in radiological examinations. However the anti-parkinsonian drug, trihexyphenidyl was effective.(ABSTRACT TRUNCATED AT 250 WORDS)