OBJECTIVE Esomeprazole is the S-isomer of omeprazole, with a stronger acid suppressive effect than omeprazole. This open, randomized crossover study was designed to evaluate the effect of esomeprazole and another proton-pump inhibitor, rabeprazole, on intragastric pH in healthy Chinese. METHODS Thirty-six healthy volunteers (26 men and 10 women, aged between 20 and 31 years) were enrolled. Subjects were given either esomeprazole 40 mg (n = 18) or rabeprazole 10 mg (n = 18) orally once daily for 5 days during the first dosing period, then the other medicine at the set dosage for the second dosing period. The two periods were separated by a 14-day washout phase. The doses were chosen according to the State Food and Drug Administration of China for the treatment of acid-related diseases. Intragastric pH was continuously monitored for 24 h on days 1 and 5 of each dosing period. CYP2C19 genotypes were analyzed to identify the extensive metabolizers (EM) and poor metabolizers (PM). RESULTS The percentage of time with intragastric pH >4 was significantly higher (P < 0.001) in subjects receiving esomeprazole than in those receiving rabeprazole in the first 4 h after administration of the first dose (70.65% vs 44.87%), at 24 h on day 1 (73.7% vs 54.8%) and at 24 h on day 5 (84.2% vs 76.2%). The median intragastric pH was also higher in subjects receiving esomeprazole than in those receiving rabeprazole in the first 6 h, day 1 and day 5 (P <or= 0.001). The percentage of subjects with intragastric pH >4 for at least 16 h on day 1 (63.9% vs 33.3%) and on day 5 (88.9% vs 61.1%) was higher after administration of esomeprazole than after rabeprazole (both P < 0.05). On genotype analysis, 28 of the subjects were EM and eight were PM. Those who were PM tended to have a higher, albeit not statistically significant, percentage of time with intragastric pH >4 and the median 24-h intragastric pH than those who were EM. Both drugs were well tolerated. CONCLUSIONS Esomeprazole 40 mg orally once daily is more effective and faster in increasing intragastric pH than rabeprazole 10 mg orally once daily, and thus offers a potential for improved efficacy in acid-related diseases.