Objective: Acid exposure to esophageal epithelium leads to hyperplasia and mucosal thickening. This is associated with upregulation of antiapoptotic genes. Recently, heat shock proteins have been implicated in esophageal mucosal response to stress. We sought to determine the influence of gastroduodenal reflux on esophageal mucosal heat shock protein 27 gene (murine analog Hspb1, human HSPB1) expression in vivo and the effect of HSPB1 overexpression on proliferation of esophageal mucosal cells in vitro. Methods: Balb/c mice underwent either anastomosis of gastroesophageal junction and first portion of duodenum to induce continuous gastroduodenal reflux (n = 14) or sham procedure (n = 12). Quantitative reverse transcriptase polymerase chain reaction was used to determine the influence of gastroduodenal reflux on Hspb1 expression. Immunofluorescent microscopy and immunoblotting were used to quantify changes in heat shock protein 27 protein expression. Lentiviral infection techniques were used to overexpress HSPB1 in human esophageal epithelial cells. Both 3-(4,5-dimethylthiazole-2-yl) 2,5,-diphenyl tetrazolium bromide and 5-bromo-2-deoxyuridine incorporation assays were used to assess cell proliferation. Results: Expressions of Hspb1 and its protein product were increased in esophageal tissue after 12 weeks' reflux relative to sham control group. Expression was located mainly in hyperplastic epithelial cells. Overexpression of HSPB1 in human esophageal epithelial cells resulted in increased proliferation. Conclusions: Heat shock protein 27 is upregulated in response to gastroduodenal reflux and is a mediator of human esophageal epithelial cell proliferation and growth. This novel finding illustrates the importance of its expression in the development of inflammation and mucosal thickening associated with esophageal reflux. © 2010 The American Association for Thoracic Surgery.