The use of NSAIDs is strongly associated withpeptic ulceration. The inhibition of prostaglandinsynthesis with the consequent increase of gastricacidity is considered a possible mechanism. Therefore we decided to assess the effect of one-monthtreatment with NSAIDs on the circadian gastric pH ofrheumatoid arthritis (RA) patients. We studied 11consecutive patients (one man and 10 women, median age55, range 26-72 years) with confirmed RA. None wasH. pylori positive. A 24-hr gastric pH recording wasperformed both in basal conditions and after one-monthtreatment with either indomethacin 150 mg/day (eight cases) or ketoprofen 300 mg/day (three cases).Only the 10 female patients were eligible for finalanalysis, and six matched healthy subjects not takingNSAIDs were used as control group. The number of 24-hr pH readings for various pH thresholds wascalculated for both populations. The highest acid levels(pH < 3.0) did not differ between the two pH profilesof the control group (7440 vs 7391, P = NS), while they predominated after the one-month NSAIDtreatment (10,339 vs 11,440, P < 0.001) in RApatients. These findings show that there is an increasedgastric acidity after one-month of treatment with NSAIDs in female patients with RA of recent onset.This may sustain the rationale of using antisecretoryagents to prevent gastroduodenal ulcerations in thesepatients.