Our aim was to evaluate the efficacy of assisted ventilation through a nasal mask (AVN) in treating chronic obstructive pulmonary disease (COPD) patients who were admitted to a pneumology ward due to decompensation, with PaCO2 > 60 mmHg and pH < 7.35. We studied 13 COPD patients who were first observed for 1-2 days until adaptation and then given 2 daily sessions of AVN lasting 4 hours with double positive pressure (DP90) devices through Sullivan mask with a cannula for hyperoxia. Gasometric readings were recorded, along with subjective assessment of condition and problems with the mask. Gasometric readings were taken as follows: the first upon admission to the ward (AW), the second with AVN 2 days after adaptation and the third 3 hours after the second (POST). Statistical analysis was with a Student t-test for paired series. Mean age was 64 +/- 3 years and FEV1 was 0.69 +/- 0.14 l. Interruptions were due to the need for mouth opening even at minimum pressures, and the inability to adapt to the consequent tachypnea. No other problems were reported by the remaining patients and all perceived improvement subjectively. The pH of 7.29 +/- 0.03 at AW increased to 7.41 +/- 0.03 with AVN (p < 0.001) and held steady at 7.39 +/- 0.01 at POST (p < 0.001 POST-AW and p = NS POST-AVN). PaO2/FiO2 was 223 +/- 49 mmHg at AW and 267 +/- 41 mmHg at the POST reading (p = 0.06). PaO2 with AVN was 67 +/- 8 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)