Conclusion: This case illustrates that pathogenesis in propionic acidemia includes cytotoxic damage to the CNS, probably caused both by trapping of organic acids (3) and lack of anaplerotic substances for the Krebs cycle (4). Reference: (1) Acute respiratory distress syndrome (ARDS) is an acute condition characterized by bilateral pulmonary infiltrates and severe hypoxemia in the absence of evidence for cardiogenic pulmonary edema. Major risk factors associated with the development of ARDS include bacteremia, sepsis, trauma, fractures, burns, massive transfusion, pneumonia, aspiration, drug overdose, near drowning, postperfusion injury after cardiopulmonary bypass, pancreatitis, and fat embolism. Organic acidemias have not been previously reported as a risk factor for ARDS. We present herein two patients with organic acidemia who were followed up with ARDS. One of them was mut0 methylmalonic acidemia (MMA) and the other was propionic acidemia (PA). They were admitted with vomiting and subsequently developed neutropenia, trombocytopenia and lactic acidosis. In within several days on emergency care, they exhibited hypoxia and respiratory insufficiency, the chest X-ray were suggestive of ARDS. Despite intensive care and ventilatory support, the patient with MMA died, the other survived.