Proton pump inhibitors such as lansoprazole are used in the treatment of gastroesophageal reflux disease (GERD), but dosing guidelines for infants have not been determined. The objective of this study was to assess the clinical efficacy of 2 dosing regimens of lansoprazole in infants with GERD using the revised infant gastroesophageal reflux questionnaire scores (I-GERQ-R). Thirty consecutive infants (3-7 months) with GERD, whose conditions were diagnosed by I-GERQ-R scores of > or =16, were randomly assigned to receive 1 of 2 lansoprazole dosing regimens: 15 mg given once per day (group A) or approximately 7.5 mg given 2 times per day (group B). Matched infants in a control group were treated with an extensively hydrolyzed formula (group C). Daily I-GERQ-R scores were gathered, and the scores after 1 and 2 weeks of treatment were used for analysis. The mean pretreatment scores were similar in groups A, B, and C (26.6, 26.9, and 25.9, respectively). After treatment there was a similar drop in the mean scores in groups A and B (20.6 and 20.0, respectively), but not in group C (25.8). At the end of the first week of treatment, in group A, 5 of 15 infants (33%) had a significant reduction in their I-GERQ-R scores, whereas in group B, 10 of 15 infants (67%) had a significant reduction in their I-GERQ-R scores (P < 0.05). At the end of the second week of treatment, groups A and B had similar numbers of patients with significant improvement (60% and 67%), which was higher than in group C (3/15, 20%). Overall, there was no difference in the symptom response, as measured by I-GERQ-R scores, between 15 mg of lansoprazole given once per day and 7.5 mg given twice per day in infants with GERD, but the twice-daily regimen produced a faster symptom response. Both regimens were significantly better than treatment of infants with an extensively hydrolyzed formula.