Background and objective: Nocturnal symptoms are common in asthma patients and have the potential for considerable clinical effects due to a lack of sleep and persistent daytime symptoms of somnolence and activity impairment. The primary objective of this investigation was to determine the effect of a 14-day course of once-daily evening administration of mometasone furoate 400 mu g administered via a dry powder inhaler (MF-DPI 400 mu g qd pm) on the overnight decline in pulmonary function observed in patients with nocturnal asthma. Methods: Eligible enrollees were between the ages of 18 and 60 years and had established mild to moderate asthma, with an improvement in forced expiratory volume in 1 second (FEV(1)) of >15% after administration of inhaled salbutamol (albuterol) 200 mu g. All enrolled patients had a history of nocturnal asthma. Enrollees were randomized to receive MF-DPI 400 mu g qd pm or placebo administered between 6pm and 8pm for 14 days. The primary outcome evaluated in the study was reduction in nocturnal decline in evening (8pm) to morning (6am) FEV(1) values. Secondary outcomes included reduction in nocturnal decline in evening to morning peak expiratory (low rate (PEER), polysomnographic indices of sleep, and psychometric indices (Nocturnal Rhinoconjunctivitis Quality of Life Questionnaire [NRQLQ], 36-item Short Form of the Medical Outcomes Survey [SF-36], and Asthma Quality of Life Questionnaire [AQLQ]). Results: A total of 20 patients were randomized and completed all phases of the study. No significant differences were observed between treatment groups in the primary outcome of nocturnal decline in FEV(1) from pretreatment to end of treatment. Likewise, there was no significant difference between treatment groups in polysomnographic indices of sleep or quality-of-life assessments. However, there was a trend toward improvement in the activity scale of the AQLQ assessment in the MF-DPI 400 mu g qd pm treatment group. Conclusion: No significant treatment effect on nocturnal pulmonary function, sleep indices or quality of life was observed with 14-day administration of MFDPI 400 mu g qd pm. These findings are limited by the small sample size and the short treatment period evaluated. Future studies are warranted to study the effects of MF-DPI therapy in patients with nocturnal asthma.