Samples of lymph nodes from 88 patients with B-cell non-Hodgkin's lymphoma (B-NHL) grouped by the Working Formulation (WF) and from 15 patients with benign lymphadenopathies were investigated immunohistochemically and ultrastructurally for changes in angiogenesis and stromal distribution of two subendothelial basement membrane (BM) components, namely laminin and type IV collagen. The microvessel number was usually low in lymphadenopathies, and increased significantly in low-grade B-NHL. Intermediate-grade tumors displayed a further significant increase that was mainly due to their diffuse subtypes rather than to the follicular subtype. High-grade B-NHL showed the highest counts. By contrast with the lymphadenopathies studied, the stroma of B-NHL reacted intensely with both BM components, whose linear co-expression was significantly associated with low-grade and follicular intermediate-grade B-NHL, while expression of laminin alone in a granular pattern was detected in diffuse intermediate-grade and high-grade tumors. Ultrastructural analysis revealed immature vessels more frequently in diffuse intermediate-grade, and in high-grade B-NHL. These in situ data suggest that angiogenesis occurring in B-NHL increases along their progression path, and emphasize the importance of angiogenesis as an epigenetic phenomenon of B-NHL progression.