The present study was undertaken to examine the cellular composition of the aortic wall in Takayasu's arteritis and to investigate the association of different cell types in the immuno-inflammatory reactions of this disease. Specimens of aortic wall affected by Takayasu's arteritis were obtained from 10 patients (five male, five female), aged 32 to 68 years (mean 49.5 years) at elective operation. The mean duration of disease was 6.5 years (range 2 months to 13 years). Specimens were embedded in paraffin and the sections stained with antibodies to CD3 (to identify T cells), CD20 (B cells), S-100 (dendritic cells), CD15 (granulocytes), CD68 (macrophages), alpha-SMA (smooth muscle cells) and von Willebrand factor (endothelial cells). Immunohistochemical examination demonstrated that all specimens showed histological alteration with the replacement of the muscular and elastic layers of the media and adventitia by dense fibrous tissue, and were characterized by varying degrees of inflammatory cell infiltration. In five cases, inflammatory nodules consisting of numerous T cells and B cells were observed in the adventitia. Within the inflammatory nodules, as well as around areas of neovascularization in the deep portion of the intima, lymphocytes were co-localized with dendritic cells. In addition, in the adventitia, the accumulation of a large number of granulocytes was observed. The present study demonstrates that immune inflammation is a typical feature of Takayasu's disease, and that the interactions between dendritic cells and lymphocytes may be important in the control of the immune reactions in this vascular pathology.