As no comparative study is available on the categorized serum pepsinogen A and C concentrations, we have measured serum pepsinogens in patients with gastric diseases and after gastric surgery. Hyperpepsinogenemia A (>120 mu g/l) occurred frequently in patients with the Zollinger-Ellison syndrome (71%) and hypertrophic gastropathy (100%), whereas hypopepsinogenemia A (<17 mu g/l) was found mostly in patients with achlorhydria (87%) and after total gastrectomy (100%). Patients with the Zollinger-Ellison syndrome frequently (58%) had hyperpepsinogenemia C (>40 mu g/l), which was also the case in all patients with hypertrophic gastropathy who had in addition a low pepsinogen A:C ratio (<1.6). Patients with achlorhydria, hypertrophic gastropathy, or after total gastrectomy fell into an aberrant category. From this study we conclude that measurement of serum pepsinogen A and C and calculation of their ratio yield information useful for differentiation of gastric abnormalities.