This is a randomised, double-blind, placebo-controlled, two-period crossover study, to investigate the efficacy of ONO-8539 on acid-induced oesophageal hypersensitivity in healthy male adult volunteers. Each subject will be randomised to ONO-8539 or placebo twice daily in the first treatment period and the alternate treatment in the second treatment period. Dosing in each period will be for 15 days.