Bi-level pressure support ventilation via a nasal mask (NIPSV) was provided to 28 consecutive unselected patients with acute respiratory failure due to exacerbation of chronic obstructive pulmonary failure (COPD). If NIPSV improved gas exchange within 2 h, it was continued. Otherwise, patients would be promptly intubated. The patients median age was 68 years (minimum 56, maximum 82). The arterial blood gas drawn before initiating NIPSV showed (FiO2 21%) a mean PaO2 of 41.3 +/- 6 mm Hg, a mean PaCO2 of 66 +/- 15 mm Hg and a mean pH of 7.31. Upon admission the mean respiratory rate was 36 breaths/min and the median Apache II score was 20.5 (minimum 13, maximum 32). Despite oxygen administration all patients failed to improve their PaO2 and/or showed a consistent and dangerous hypercapnic response. NIPSV was performed with a median inspiratory positive airway pressure of 14 cm H2O (minimum 10, maximum 20) and a median expiratory positive airway pressure of 4 cm H2O (minimum 3, maximum 6). Eighteen patients (64%) were successfully ventilated with NIPSV, while in 10 (36%) NIPSV failed. A high Apache II score, but not admission blood gas exchange or respiratory rate, seems to be correlated with the failure to ventilate with NIPSV. The results of our preliminary experience suggest the use of NIPSV as an initial approach to acute respiratory failure due to exacerbation of COPD, particularly in patients with an Apache II score of less than 29.