A single-blind, randomized endoscopic tolerance study was conducted to compare daily doses of flurbiprofen (Ansaid, Upjohn) at 100, 150, and 200 mg per day with 2,600 mg of aspirin per day. Ten normal volunteers were enrolled in each of the flurbiprofen groups, and five were enrolled in the aspirin group. Analysis of the mean gastric mucosal injury scores obtained on day eight revealed statistically significant lower mean scores (p = 0.05) in the 100-mg and 150-mg flurbiprofen treatment groups when compared with the 200-mg flurbiprofen group and the aspirin group. No significant differences were found between any of the treatment groups in duodenal mucosal injury scores. Mean scores for gastric mucosal injury in the three groups receiving flurbiprofen showed a definite dose relationship. The aspirin-treated subjects had significantly decreased uric acid levels (p = 0.006) and a significantly higher incidence of tinnitus (p = 0.04) compared with the flurbiprofen treatment groups. There was a poor correlation between subjective symptomatology and endoscopic pathologic findings.