The hydrophobic properties of the gastric mucosa are reduced by NSAIDs and by Helicobacter pylori infection. Our investigation was to determine whether this abnormality was due to the bacteria or to the inflammatory response. Contact angle measurements were made on gastric antral and corpus biopsies taken from 10 H. pylori-infected volunteers before eradication therapy, after 2 and 14 days of therapy, and 4 weeks after therapy. The contact angle improved steadily and statistically throughout the 2 weeks of therapy (for day 0, 3, 14, respectively) antral mucosa 54.2 +/- 2, 59.3 +/- 2, and 63.2 +/- 2; corpus mucosa 55 +/- 1, 57.8 +/- 3, and 66.6 +/- 1. After 2 days of therapy, H. pylori bacteria were no longer evident, and yet the contact angle continued to improve, suggesting that bacteria and bacterial products (e.g., lipases) may not be critical factors. H. pylori was eradicated in five and failed in five. One month after ending therapy, the contact angles of those with recrudescence of infection and those with eradication were similar and higher (p < 0.05) than before therapy (antrum: 69.8 +/- 1 vs. 71.1 +/- 2, corpus: 66.4 +/- 4 vs. 70.8 +/- 2) (p > 0.25 for both). We conclude that gastric surface hydrophobicity abnormalities do not appear to be directly related to the presence of H. pylori organisms or the histologic features of acute inflammation, but are responsive to antimicrobial therapy.