Using an extended indirect immunoperoxidase method and the lectin I of Ulex europaeus ( UEA -I), whose binding sites in lymph nodes are restricted to endothelial cells and erythrocytes, the angioarchitecture of 31 lymph nodes affected by Hodgkin's disease (HD) was demonstrated and analyzed. Compared with the normal state, the lymphocytic predominance type has a low relative vascular density, and venular endothelium is epithelioid throughout. Mixed cellularity types, especially those rich in epithelioid cells, have the lowest relative vascular density; the venular endothelium is often flat. In the sclerosing areas of the nodular sclerosis type structurel differences between capillaries, arterioles and venules vanish. Due to parenchymal atrophy and cellular depletion, relative vascular density is markedly increased in such areas, as is the case in lymphocytic depletion types. Despite all the histomorphological changes occurring in HD, the vascular system of the lymph node, surprisingly, does not undergo profound alteration. There is a positive correlation between the degree of epithelioid transformation of venular endothelium and trans-venular lymphocytic traffic. The conditions are described under which the otherwise non-reactive sinus endothelium expresses the UEA -I receptor.