Chronic atrophic gastritis, which is though to be a high risk for gastric cancer, can be diagnosed by serum pepsinogen levels. We compared the usefulness of the measurement of pepsinogen levels and indirect photofluorography as indicators of gastric cancer in a mass screening involving 5,620 Japanese subjects (mean age: 60.1 years old; male : female = 2,268:3,352) in 1991 and 1992. Subjects with a serum pepsinogen I level below 30 micrograms/liter or a pepsinogen I/II ratio below 2.0 were considered to be at high risk of gastric cancer. The incidence of gastric cancer and the ratio of early cancers detected by pepsinogen levels (0.12%, 4/7) were similar to those detected by photofluorography (0.11%, 4/6). Our results showed that mass screening using pepsinogen levels was as useful as indirect photofluorography for the detection of gastric cancer in Japan. In addition, our results showed that the sensitivity of gastric mass screening was increased when the measurement of serum pepsinogen levels was combined with photofluorography.