BACKGROUND: Symptoms of chronic obstructive pulmonary disease may vary throughout the day and it is important that therapeutic approaches provide 24-h symptom control. We report the results of two phase IIIb crossover studies, PT003011 and PT003012, investigating the 24-h lung function profile of GFF MDI (glycopyrrolate/formoterol fumarate 18/9.6 µg delivered using innovative co-suspension delivery technology) administered twice daily. METHODS: Patients with moderate-to-very severe chronic obstructive pulmonary disease received 4 weeks' treatment with each of GFF MDI, placebo MDI, and open-label tiotropium (PT003011 only). Lung function was assessed over 24 h on day 29 of each treatment period. The primary outcome was forced expiratory volume in 1 second area under the curve from 0 to 24 h (FEV1AUC0-24). Other outcomes included change from baseline in average daily rescue medication use over the treatment period. In addition, we conducted a post-hoc analysis of data pooled from both studies to further characterize the effect of GFF MDI on inspiratory capacity. RESULTS: GFF MDI treatment significantly increased FEV1AUC0-24 versus placebo in studies PT003011 (n = 75) and PT003012 (n = 35) on day 29 (both studies p < 0.0001), with similar improvements in FEV1AUC versus placebo for hours 0-12 and 12-24. In PT003011, improvements with GFF MDI versus tiotropium in FEV1AUC were greater during hours 12-24 compared to 0-12 h. GFF MDI treatment also resulted in a significant reduction in rescue medication use versus placebo (-0.84 [p<0.0001] and -1.11 [p=0.0054] puffs/day in PT003011 and PT003012, respectively), and versus tiotropium in PT003011 (-0.44 [p=0.017] puffs/day). A post-hoc pooled analysis showed patients treated with GFF MDI were more likely to achieve a >15% increase from baseline in inspiratory capacity than patients treated with placebo or tiotropium (72.1%, 19.0% and 47.0% of patients, respectively after the evening dose on day 29). There were no significant safety/tolerability findings. CONCLUSIONS: GFF MDI significantly improved 24-h lung function versus placebo in patients with moderate-to-very severe chronic obstructive pulmonary disease, with similar benefits in the second 12-h period compared to the first, supporting twice-daily dosing of GFF MDI. TRIAL REGISTRATION: Pearl Therapeutics, Inc.; www.clinicaltrials.gov ; NCT02347072 and NCT02347085 . Registered 21 January 2015.