Susceptibility to Helicobacter pylori infection is a poorly understood phenomenon. This study was undertaken to establish whether either smoking or chronic non-steroidal anti-inflammatory drug (NSAID) consumption might in some way predispose to H. pylori infection and hence lead to peptic ulceration. Serological evidence of H. pylori infection was assessed in 100 consecutive subjects receiving NSAIDs without any evidence of gastrointestinal upset and 100 matched controls. All subjects had a full assessment of their smoking habits. Sixty-three per cent of patients taking NSAIDs compared to 51% of controls had evidence of H. pylori infection (NS). Smoking habit also had no effect on H. pylori colonization. The ulcerogenic potential of NSAIDs and smoking does not appear to be mediated via a prediposition to H. pylori infection.