Objective: To determine the effect of the lung surfactant (Surfacen ® ) in the recovery of the oxygenation in adults with acute re- spiratory distress syndrome (ARDS). Material and methods: Adults between 18 and 75 years with acute respiratory distress syndrome, were included (48 patients) in a clinical trial phase II, controlled, randomized and multicentric. A group (24) received treatment of lung surfactant every eight hours, during three days, in dose of 100 total mg, next to the standard treatment (oxygenation and ventilation mechanics). The group control (24) alone received the standard treatment. The effect was evaluated through the index PaO 2 /FiO 2 , compliance (Cs) and the thorax X-Ray. Other studied variables were the mortality, days of intubation, of ventilation mechanics (VM) and of stay in the Unit of Intensive Cares (UCI). Results: It existed differences statistically signifi cant (p=0.0399) among the groups in the index PaO 2 /FiO 2 , compliance (p = 0.005). There were not statistical differences in the thorax X-Ray (p = 0.7177), the mortality (p = 0.3652), days of intubation endotracheal (p = 0.2659), of ventilation mechanics (p = 0.3582) and stay in the UCI (p = 0.2941). Conclusions: The use of the lung surfactant (Surfacen ® ) next to the standard treatment in adults with ARDS improved oxygenation signifi cantly.