This study is the second phase of a RCT study that attempts to employ the stem cells isolated from the embryonic membranes as a strategy for treatment of patients with acute respiratory distress syndrome. To achieve this goal, three groups (each group includes 5 cases) suffering from acute respiratory syndrome referred to two hospitals in Tehran (Shariati and Imam Khomeini) will be selected. Inclusion criterion is patients with age >18. On the other hand, exclusion criterion would be any acute and systemic infections like HIV, Hepatitis B and C. The first, second, and third groups will intravenously receive 1000000/kg, 2000000/kg, and 5000000/kg embryonic stromal cells, respectively (each injection should take 30 minutes). Patients will be monitored by ICU specialists for possible complications immediately after injections. Indeed, the major complication in this study is expected to be the elevation in patient's doses of vasopressors (norepinephrine, phenylepinephrine, dopamine, epinephrine, etc.) Other complications are post-injection clinical instabilities especially in cardiac and respiratory systems, together with dose-limiting toxicity. It should be mentioned that no blinding will be utilized for evaluation of these complications.