Serum pepsinogen levels were examined in 107 patients with gastric carcinoma, by immunoradiometric assay for evaluating its clinical usefulness in gastric cancer. The mean serum pepsinogen-I (PG-I) level and the pepsinogen-I/pepsinogen-II (PG-I/II) ratio decreased as the histologic stage increased. Also, serum pepsinogen-II (PG-II) correspondingly increased with the increase of histologic stage. Moreover, in patients with low PG-I/II (<2.0), prognosis was significantly poorer than in those with high PG-I/II (greater-than-or-equal-to 2.0). The rate of recurrence after a curative resection was significantly higher in patients with low PG-I/II. These results suggest that measurement of serum pepsinogens and calculation of PG-I/II are useful for prediction of the tumor stage, and PG-I/II may be a prognostic indicator for gastric carcinoma.