To investigate the involvement of tenascin (TN) in human neointimal hyperplastic lesion formation, we studied 12 human arteriovenous (AV) polytetrafluoroethylene (PTFE) loop grafts removed at the time of graft revision. Immunoperoxidase technique was used to determine TN and proliferating cell nuclear antigen (PCNA) as an index of cell proliferation. The venous anastomotic neointimal hyperplastic lesion was analyzed as three layers, each one-third of the thickness. TN was distributed in the neointima as follows: (1) in the luminal layer, all lesions were intensely stained; (2) in the middle layer, 9 of 12 (75%) lesions had moderate reactivity; (3) in the deep layer near the PTFE grafts, 3 of 12 (25%) lesions were strongly stained and 5 of 12 (42%) had moderate reactivity; and (4) 90 +/- 6% of microvessels within the neointima showed intense periendothelial staining. PCNA indices were as follows: luminal layer, 29 +/- 11%; middle layer, 9 +/- 5%; deep layer near the graft, 9 +/- 7%; and microvessel containing intimal fields, 67 +/- 4%. The cell proliferation rate was significantly higher in the luminal layer than in the middle or deep layers of neointima (P < 0.05). The PCNA index in microvessel-containing intimal fields was three to eight times that of avascular fields (P < 0.001). These data demonstrate that TN is distributed in a pattern similar to that of cell proliferation in human neointimal hyperplastic lesions. The results suggest that TN expression may have a potential role in neovascularization and neointimal growth in human AV PTFE graft failure.