BACKGROUND The aim of this paper was to investigate the effectiveness of three different recruitment maneuvers (RMs) on respiratory and hemodynamic indexes, in patients with acute respiratory distress syndrome (ARDS), and determine the impact of patients' body mass index (BMI) on RMs efficacy. METHODS This was a prospective clinical trial conducted in a general intensive care unit. In 25 consecutive early ARDS patients arterial blood gases, respiratory system elastance (Est,rs) and hemodynamics were monitored before (T(0)), and at 3, 15, and 30 min (T(3), T(15), T(30), respectively) after each of three different RMs techniques with same airway pressures (45 cmH(2)O), randomly applied in each patient; RM-1: pressure control ventilation for 1 min, RM-2: two hyperinflations with continuous positive airway pressure for 20 sec and 1 min interval in between, RM-3: three consecutive sighs. RESULTS All RMs improved oxygenation and Est,rs shortly (T(3)) after their application, but only RM-2 had a prolonged beneficial effect on oxygenation (T(30)). Patients were further divided according to their BMI: in the low BMI group (<27.3 Kg/m(2)) the effectiveness of RMs was similar to the whole study population, while in the high BMI group (≥ 27.3 Kg/m(2)) no sustained effect followed any RM. CONCLUSION In our cohort, recruitment by two sustained inflations resulted in a more persistent improvement of oxygenation as compared with recruitment by pressure controlled ventilation or consecutive sighs with the same airway pressure. BMI seems to have an impact on RMs effectiveness, most probably by altering the effective transpulmonary pressure. More studies are required to elucidate this observation.