Serum spermidine was assayed by radioimmunoassay in different stages of esophageal carcinogenesis in the population from high risk area of esophageal cancer, Linxian County. The serum spermidine values were 76.94 +/- 74.38 ng/ml in 36 normal individuals; 115.71 +/- 113.45 ng/ml in 35 patients with marked epithelial hyperplasia (MEH) and 294.48 +/- 135.36 ng/ml in 31 patients with early esophageal cancer. Patients with MEH were given intervention treatment by Aminoretinoic Ester or Anticancer B or placebo (Starch) as controls. One year later, samples from the population were collected again for serum spermidine measurement. The values were 95.8 +/- 68.2 ng/ml in 27 normals; 125.1 +/- 72.9 ng/ml in 62 patients with MEH treated by Anticancer B; 125.6 +/- 117.2 ng/ml in 64 patients with MEH by Aminoretinoic Ester; 162.4 +/- 76.6 ng/ml in 62 controls and 210.5 +/- 182.9 ng/ml in 44 patients with early esophageal cancer. The results showed that spermidine radioimmunoassay could reflect the tendency of esophageal precancerous changes toward cancer or back to normal. They can be taken as a mid-way monitor indicator for tumor-blocking drugs. Also, it could be of value in the early diagnosis of esophageal cancer.