Abstract We used immunohistochemical techniques to study the distribution of transforming growth factor-β 1 (TGF-β 1) and infiltrating lymphocytes and macrophages in human astrocytomas. Thirteen of 15 grade 4 astrocytomas (glioblastomas) showed staining with anti-TGF-β 1 antibody, predominantly in proliferating endothelial complexes and surrounding small and medium-sized blood vessels. Brain tissue microscopically free of tumor cells (n = 8) and more differentiated astrocytomas of varying grade (1 to 3; n = 6) devoid of endothelial proliferation did not stain with anti-TGF-β 1. Normal brain contained only rare lymphoreticular cells. The majority of astrocytomas studied, however, contained T lymphocytes and macrophages with smaller numbers of B lymphocytes. The lymphoreticular infiltrates were concentrated primarily in close proximity to blood vessels. Within an individual tumor perivascular regions staining for TGF-β 1 never contained more than occasional T lymphocytes. Perivascular regions not staining for TGF-β 1 frequently contained low to high numbers of T lymphocytes. The inverse relationship in the distribution of TGF-β 1 and lymphocyte infiltrates is compatible with a functional relationship between this cytokine and an immune effector cell response to glioblastomas.