Serological evidence of infection with Helicobacter pylori may predict gastrointestinal intolerance to non-steroidal anti-inflammatory drug (NSAID) treatment in rheumatoid arthritis. Specific circulating antibodies to the spiral gastric organism, Helicobacter pylori (HP) were detectable in 43% of 68 patients with rheumatoid arthritis by complement fixation test (CFT) and enzyme-linked immunosorbent assay (ELISA), a frequency comparable with that of a normal, age-matched population. Presence of these antibodies correlated strongly with a previous history of peptic ulcer disease (PUD) and to the severity of NSAID-related dyspeptic symptoms, the latter often leading to multiple drug intolerance. This contrasts with short term, prospective NSAID toxicity data, which show little relationship between ulceration and HP carriage. This result suggests, however, that HP may have a definite role in the pathogenesis of symptomatic PUD associated with more chronic NSAID usage, and may have important implications for ulcer prophylaxis in these patients. 