There are surprisingly limited data regarding normal counts or distribution of eosinophils in the gastrointestinal tract, despite the increasing incidence of eosinophilic gastrointestinal tract diseases. Moreover, there are no published reports on the eosinophil number throughout the gastrointestinal tract of adults or Asian populations, or those investigating the effect of race on eosinophil count. First, in our study, the number of eosinophils from each portion of the gastrointestinal mucosa was quantified on biopsy slides from a Japanese adult population (132 samples). Next, the surgical resections from Japanese (110 samples), Japanese Americans (64), and Caucasians (57) were used to investigate the racial and environmental effects. Our results with the Japanese biopsy samples showed a significant increase in the number of eosinophils from the esophagus to the right colon (mean±SD/mm: 0.07±0.43 for the esophagus, 12.18±11.39 for the stomach, and 36.59±15.50 for the right colon), compared with a decrease in the left colon (8.53±7.83). Investigation using surgical samples showed that the distribution patterns in the gastrointestinal tract were very similar among the 3 ethnic groups, and there were no significant differences in the number of eosinophils among these groups, except in the esophageal epithelium. This study is the first report on the normal numbers and distribution of eosinophils throughout the gastrointestinal tract not only of an Asian population but also of adults. Our data suggest that a cutoff value for eosinophil counts, when rendering a diagnosis of eosinophilic gastrointestinal tract disease, should be individualized to the different biopsy sites. Interestingly, race and environmental factors did not seem to have a significant effect on eosinophil densities and distributions.