SUMMARY Paracetamol has replaced aspirin as the analgesic of choice in many situations. The major reason is the damaging effect of aspirin on gastric mucosa. Alterations in gastric ionic fluxes and potential difference provide measures of aspirin-induced structural damage. We studied the effect of large doses of paracetamol (acetaminophen 2-0 g) on gastric ionic fluxes in man. In addition, the effect of 2-0 g paracetamol on gastric potential difference was compared with that of 600 mg aspirin. (Goulston and Skyring, 1964). Vickers in 1967 found a 17% incidence of visible gastroscopic lesions after aspirin compared with 0% after paracetamol. This study, however, seriously underestimated the incidence of aspirin-induced damage as measured by other techniques (Goulston and Skyring, 1964) including microscopic examination of gastric biopsies (Ivey et al., 1975a), which indicated damage in 100% of subjects.Aspirin has been well documented to damage