Non-invasive mechanical ventilation (NIMV) has been recently applied to patients with acute respiratory failure (ARF) complicating chronic pulmonary disease or other medical disorders mainly in ICUs. This study aims at evaluating the efficacy of NIMV in patients with ARF in a Pulmonary Department of a general hospital. Twenty-one patients with hypercapnic respiratory failure (Group A, 16 pts) or hypoxaemic respiratory failure (Group B, 5 pts) were treated with NIMV via a nasal or facial mask connected to a BiPAP ventilatory device, in order to avoid intubation and improve gas exchange. In 21 patients of group A, PaO2 improved (from 45,1±8 to 62,8 ±10,5 mmHg, p<0,001), PaCO2 decreased (from 83,5±15,4 to 65,7±11,4 mmHg, p <0,001) and pH improved (from 7,25±0,04 to 7,37±0,06, p<0,001). Four patients failed to improve and were transferred to the ICU in order to receive invasive mechanical ventilation. PaO2 improved in all patients of group B (from 35,6±6,5 to 63,6±7,3 mmHg under NIMV). None of them needed invasive mechanical ventilation. The mean duration of NIMV was 48,9±35,7h in group A versus 90,8±46,7h in group B. The mean length of hospitalization was 11,3±9,1 and 14,8±8,2 days respectively. NIMV could be introduced in every day clinical practice in the treatment of ARF in a Pulmonary Department. Especially in cases of acute exacerbations of chronic respiratory insufficiency as in COPD, it can reduce the need of intubation and subsequent invasive mechanical ventilation. Pneumon 2001, 14 (2): 126-132