Indirect pieces of evidences indicate the correlation between insulin level and pathogenesis of peptic ulcer. In the present study, serum insulin releasing level after glucose loading was determined in 16 patients with duodenal ulcer (DU) using radioimmunoassay, and was compared with that of normal controls. The peak insulin level (PIL) in DU patients was significantly higher than that of normal individuals (P less than 0.05), the measurements of gastric acidity, insulin level and the gastroscopic examination were carried out both before and after the treatment. The rebound phenomenon of gastric acidity (BAO) was correlated to that of PIL (r = 0.85). The possible relationship between insulin level and DU was discussed.