Ammonia is a colorless alkaline gas with a sharp pungent odor. It is widely used in industry and there are several case reports on deleterious pulmonary damage. Ammonia is also highly neurotoxic that interferes energy metabolism in the brain even with a small amount and causes encephalopat hy in patients with severe liver disease.

We experienced two patients with toxic encephalopathy and followed- up for 18 months. We assumed that ammonia was supposed to play a major role in the dysfunction of their brains. In our cases, the possible mechanisms of brain damage are as followings: ⸁ ammonia has direct toxic effect on brain by altering the energy metabolism, ⸂ inhalation of ammonia results in severe pulmonary damage and it may aggravate brain injury, and ⸃ besides ammonia itself, relatively hypoxic environment that they were exposed can take part in the brain injury.