RATIONALE: Gastroesophageal reflux disease (GERD) is common in patients with asthma, suggesting an interaction between the two conditions. OBJECTIVES: To assess the effect of gastric acid suppression with the proton pump inhibitor esomeprazole on asthma outcomes in subjects with persistent moderate to severe asthma treated with antiinflammatory asthma medication. METHODS: In this double-blind study, subjects were randomized to receive esomeprazole 40 mg or placebo twice daily for 16 wk. According to nocturnal respiratory symptoms (NOC) and GERD, subjects were divided into three strata: GERD-/NOC+, GERD+/NOC-, and GERD+/NOC+. MEASUREMENTS AND MAIN RESULTS: A total of 770 subjects were randomized. There was no statistically significant improvement in morning peak expiratory flow (PEF) over placebo in the overall study population: 6.3 L/min (p = 0.061). Over the whole treatment period, in GERD+/NOC+ subjects (n = 350), esomeprazole provided an 8.7-L/min improvement (p = 0.03) in morning PEF, and a 10.2-L/min improvement (p = 0.012) in evening PEF over placebo. Among 307 subjects taking long-acting beta2-agonists, improvements over placebo were observed in morning PEF (12.2 L/min, p = 0.017) and in evening PEF (11.1 L/min, p = 0.024); these improvements were more pronounced in GERD+/NOC+ subjects. Esomeprazole 40 mg twice daily was well tolerated and no safety concerns were noted. CONCLUSIONS: Esomeprazole improved PEF in subjects with asthma who presented with both GERD and NOC. In subjects without both GERD and NOC, no improvement could be detected.