To determine whether dietary calcium supplementation affects esophageal precancerous lesions, 200 subjects with esophageal lesions in a high-risk area for esophageal cancer in China (Huixian, Henan) were randomly divided into 2 groups (100 subjects/group). Subjects in one group received an oral supplementation of calcium carbonate tablets (1200 mg of calcium daily), and subjects in the other group received placebo pills for 11 months. At the entry and the end of the trial, esophagoscopy was performed, and 2 or 3 biopsy specimens were taken from the middle and lower thirds of the esophagus and from macroscopic lesions, if any, of each subject for histopathology and cell proliferation analysis with deoxythymidine labeling. In comparison to normal epithelium, increased proliferative compartment size was observed in epithelia with hyperplasia or dysplasia. After the intervention, the percentage of individuals with "normal epithelium," "basal cell hyperplasia," "basal cell hyperplasia II," and "basal cell hyperplasia III and dysplasia" were 44, 31, 13, and 11% in the calcium group and 35, 39, 17, and 6% in the placebo group, respectively. The labeling index was 0.046 in the calcium group and 0.044 in the placebo group. After the intervention, the labeling index in basal cell layers 1 to 5, the major zone of cell proliferation, fell 38% in the calcium group and 44% in the placebo group from before the intervention. Therefore, in this study, calcium supplementation was not shown to have beneficial effects in alleviating precancerous lesions and abnormal cell proliferation patterns.