Twenty-four-hour esophageal pH monitoring was performed in 59 children with symptoms of gastroesophageal reflux using a miniature pH electrode and a portable recording system to establish the diagnosis. Significant reflux was seen in 26 (44%) of the patients and these were treated for six weeks with cimetidine, Gaviscon, and Nestargel. Five children who did not improve either symptomatically or on repeat pH monitoring while on treatment underwent antireflux surgery. The pretreatment reflux index in this group was 26.5 compared with a pretreatment reflux index of 11.2 in the 21 patients who improved on therapy (P less than 0.01). Esophageal pH monitoring has enabled selection of children for surgery and may be used as an early indicator of those who will not benefit from long-term medical therapy. Ambulatory and home monitoring techniques are more convenient and cost-effective and allow studies to be performed in the normal home environment.