The present study explored the 24-hr variations in serum gastrin and pepsinogen in clinically healthy subjects and in patients with gastric ulcer, duodenal ulcer, and erosive gastroduodenopathy. Time-qualified data were analyzed by means of cosinor procedures. Significant changes in rhythmometric properties were documented in patients with peptic disease when compared to clinically healthy subjects. In essence, it was discovered that gastric ulcer patients exhibit a higher mesor and amplitude for both gastrin and pepsinogen, whereas duodenal ulcer patients and those with erosive gastroduodenopathy show only a significant increase in the pepsinogen mesor. These characteristics are so specific in the groups investigated that one can hypothesize that the disorders in the circadian rhythmicity of gastrin and pepsinogen have a role in determining the clinical manifestations of peptic disease.