To determine whether primary B-cell gastric lymphoma (GL) is one entity, we examined the expression of three adhesion molecules in the microvasculature of lymphomas. Stromal cells, including vascular endothelial cells, within lymphoid follicies of the gastric mucosa were also investigated. Twenty-two surgical specimens of GL were classified into low-grade malignant lymphoma arising from mucosa-associated lymphoid tissue (low-grade lymphoma, n = 9), and high-grade malignant lymphoma with (secondary high-grade lymphoma, n = 6) or without (primary high-grade lymphoma, n = 7) a low-grade component. The proportion of venules positive for ELAM-1 or VCAM-1 was significantly higher (P < 0.001) in primary high-grade lymphoma than in low-grade and secondary high-grade lymphomas. In gastric lymphoid follicles, the stromal cells of the germinal centre (GC) were positive for ICAM-1, ELAM-1, and VCAM-1, but the stromal cells of the marginal zone (MZ) were positive only for ICAM-1. We found two patterns of adhesion molecule expression in gastric lymphoid follicles, the MZ pattern and the GC pattern. Low-grade and secondary high-grade lymphomas, which had the MZ pattern, might be of MZ-cell lineage, but most primary high-grade lymphomas, which had the GC pattern, might be of follicular centre cell lineage.