We have determined the prevalence of pepsinogen II (PG II) immunoreactive cells in a large series of early and advanced gastric cancers and relationships among PG II-positivity, tumor histologic type, extent of gastric wall invasion, and presence of lymph node metastases. Of the 316 cancers evaluated, 150 (47%) expressed PG II. The prevalence by histologic type was 55% in 146 glandular tumors, 43% in 83 diffuse tumors, 16% in 25 mucoid tumors, and 51% in 59 mixed-type cancers. Two parietal cell cancers and one undifferentiated cancer were PG II-negative. In glandular and diffuse cancers, but not mucoid and mixed tumors, both the extent of gastric wall invasion and incidence of lymph node metastases were associated positively with PG II expression by the primary tumor. In particular, PG II-reactive cells were found significantly more often in advanced than in early diffuse cancers (P less than 0.05) and significantly more often in submucosal early cancers than in intramucosal early cancers (P less than 0.01). The prevalence of PG II expression also was higher significantly in metastatic cancers than in nonmetastatic cancers. This was true for advanced gastric cancers as a whole (P less than 0.01), advanced glandular-type cancer alone (P less than 0.01), advanced glandular- and diffuse- type cancers together (P less than 0.001), and early diffuse-type cancer (P less than 0.05). Only four (3%) of 145 cancers evaluated for pepsinogen I (PG I) were positive, and each also was positive for PG II. The results suggest that the expression of PG II by glandular and diffuse types of gastric cancer may be a marker of increased malignancy.