The incidence of alkaline gastroesophageal reflux (GER) was examined in 111 consecutive children referred for evaluation of GER during a 1-year period. The results of 24-hour pH monitoring studies and the medical records were retrospectively evaluated. Acid reflux was defined as occurring whenever the pH was less than 4 and alkaline reflux was defined whenever the pH was greater than 7. The percentage of time that reflux occurred, the number of reflux episodes, the number of episodes greater than 5 minutes, and the longest episode were all recorded. Based on these data, four categories of patients were identified as compared with normal values as determined by Pellegrini et al. When using criteria based on the percentage of time that reflux occurred, the largest group of children with GER was found to reflux acid (50%). However, 27 children (24%) had combined acid and alkaline reflux. Eighteen (16%) had predominantly alkaline reflux. Previously, these 18 children would have been considered as having a low likelihood of reflux by pH criteria. Endoscopic examination showed that pathological evidence of esophagitis occurred in four of the children with pure alkaline reflux. This review shows that symptomatic GER in infants and children may be due to acid or alkaline secretions or a mixture of both. A previously unrecognized cohort exists of children who demonstrate primary alkaline reflux. These patients need to be recognized and may benefit from a therapeutic program specifically designed to control alkaline reflux.