Some patients with chest wall diseases (CWD) without respiratory failure manifest important alterations in nocturnal gas exchange, as a previous stage to the future development of daytime respiratory failure. The purpose of this study was to evaluate the efficacy of nasal intermittent positive pressure ventilation (NIPPV) during sleep in a group of obese patients and in another group with restrictive thoracic diseases (RTD), comparing the results with those obtained from conventional nocturnal oxygen therapy. From a total of 42 patients with CWD free of daytime respiratory failure, 27 (64%) were considered nocturnal oxygen desaturators without sleep apnea and were included in the study. The study protocol was completed by 21 of these patients. After 2 weeks of treatment, symptoms of dyspnea, morning headaches, and morning obnubilation improved significantly (p<0.05) in both groups of patients after NIPPV but not with oxygen. Baseline daytime PaO2 was 68+/-7 mm Hg in the obese group of patients and 73+/-11 mm Hg in the RTD group. It improved significantly with NIPPV to 73+/-5 mm Hg in obese patients (p<0.05) and to 77+/-12 mm Hg in the RTD group (p<0.05) but did not change with oxygen (68+/-8 mm Hg in the obese group and 73+/-12 mm Hg in the RTD group). Both treatments improved oxygen saturation during sleep, but oxygenation tends to be higher with oxygen than with NIPPV. Only NIPPV was able to normalize the baseline nocturnal alveolar hypoventilation. From the 21 patients treated, 19 decided to continue with long-term NIPPV, one with oxygen, and one refused treatment. We conclude that in patients with CWD who manifest nighttime oxygen desaturation and hypoventilation, early initiation of NIPPV is preferable to supplemental oxygen. Our results also suggest that NIPPV initiated before overt ventilatory failure could prevent its onset.