BACKGROUND Gastric mucosal surface hydrophobicity (GMSH) is an essential component of the mucosal defence system that is decreased by Helicobacter pylori and non-steroidal anti-inflammatory drugs (NSAIDs). Gastric ulcers occur predominantly in elderly subjects, and may thus reflect diminished mucosal resistance. OBJECTIVE To investigate whether aging decreases GMSH. METHODS One hundred and twenty patients without peptic ulcer disease were divided into three age groups: I (41 years or below); II (41-64 years); and III (65 years or above). METHODS Biopsy specimens were taken from the antrum, corpus, and cardia for histology (Sydney system), urease testing for H pylori, and for contact angle measurement of GMSH with a goniometer. The presence of specific H pylori antibodies was checked by immunoblotting. RESULTS Fifty two patients (43%) were infected, and 68 were uninfected with H pylori. GMSH at all biopsy sites was lower in H pylori infected subjects (p=0.0001), but also decreased with age independently of infection status (p=0.0001). The most notable decrease in GMSH occurred between age groups I and II in those with, and between age groups II and III in those without, H pylori infection. GMSH was greater in antral than in corpus mucosa in both infected (p=0.0001) and uninfected patients (p=0.0003). CONCLUSIONS A physiological decrease in GMSH with aging may contribute to the risk of ulcer development in the elderly, and may act synergistically with H pylori and/or NSAIDs on gastric mucosal defence.