A randomized double blind intervention trial was carried out in Huixian County Henan Province, a high risk area for esophageal cancer, to observe the effect of oral calcium supplementation on esophageal precancerous lesions. Two hundred and fourteen cases with basal cell hyperplasia and 40 with dysplasia of the esophagus aged 25-75 randomly received daily oral supplementation of 600 mg calcium or placebo for 7 months. In the calcium supplementation group, the basal cell hyperplasia and dysplasia of the esophagus were significantly improved and the profile of esophageal epithelial proliferation cells labeled with 3H-TdR approached that of the normal subjects in low risk area for esophageal cancer. The results indicate that calcium supplementation can inhibit basal cell hyperplasia and dysplasia of the esophageal epithelium in high risk area for esophageal cancer. The mechanism of interruption of esophageal precancerous lesions by calcium is discussed.