The purpose of this study was to assess the efficacy of bi-level positive airway pressure (BiPAP) ventilation through a nasal mask in the treatment of eight patients with hypoventilatory respiratory failure and nocturnal CO2 retention. Nocturnal CO2 retention was significantly reduced in all patients with the application of BiPAP during sleep (p less than 0.01). Daytime somnolence was relieved and dyspnea improved after three months of home BiPAP therapy. All patients tolerated home BiPAP therapy, and two patients who had previously been treated with volume ventilation via nasal mask found BiPAP more comfortable. There were no changes in FEV1 or FVC after three months of BiPAP. Daytime PaCO2 improved slightly or remained stable in all patients after three months of home BiPAP. BiPAP nasal ventilation is effective in reducing nocturnal CO2 retention short term in hypoventilatory respiratory failure due to obesity hypoventilation syndrome, chest wall restriction, or neuromuscular disease. Further studies in patients with COPD may be warranted.