We hypothesize that OSAS contribute to the symptoms related to nocturnal asthma and that CPAP therapy would improve the asthma symptoms, airway hyperactivity and quality of life in patients with nocturnal asthma and OSAS. We aim to assess (1) asthma control, airway responsiveness, daytime sleepiness, cognitive function and health status at baseline and at 3 months after nasal CPAP treatment among our asthma patients with nocturnal symptoms and OSAS; (2) the acceptance and compliance of nasal CPAP treatment.