The expression of Group-II phospholipase A2 (M-PLA2) was analysed immunohistochemically in malignant, non-malignant (including atrophic, hyperplastic, pseudopyloric metaplastic and intestinal metaplastic) and normal human gastric mucosae. M-PLA2 was consistently detected in the stem cell lineage, pseudopyloric metaplasia and the generative cells of hyperplastic foveolar epithelium and intestinal metaplasia (IM). In IM, the appearance of M-PLA2 was found to be closely related to the degree of development of the brush borders on columnar cells and was especially prominent at dense brush borders. Paneth cells of IM, particularly their secretory products, were strongly immunoreactive for M-PLA2. In gastric cancer, the expression of M-PLA2 was detected exclusively in cancer cells with a low grade of differentiation, and seemed to be intensified in the invading zone of the tumour. These observations suggest that the expression of M-PLA2 is associated with the proliferative kinetics and regeneration of human gastric mucosa, and may indicate a physiological relationship between its expression and metaplasia of small intestinal type. Moreover, the appearance of M-PLA2 may be related to the invasive ability of gastric cancer.