Frozen sections of 21 gliomas were analysed to characterize inflammatory infiltrating cells, HLA-DR antigen expression and cytokine secretion. Mononuclear cells infiltrating the tumours were mostly macrophages, which were detected in 100% of cases, and expressed HLA-DR antigens. Lymphocytes were less frequently seen and expressed the CD8 phenotype. Interleukin-1 beta (IL-1 beta) and Interleukin-6 (IL-6), two cytokines mainly produced by activated cells of the macrophage lineage, were demonstrated especially in neoplastic astrocytes. IL-1 beta immunoreactivity was detected in all tumours, and was prevalent in more anaplastic gliomas; IL-6 was found in anaplastic gliomas and in glioblastomas. IL-1 receptors were expressed by both infiltrating macrophages and neoplastic astrocytes in the gliomas analysed. These findings suggest that cytokine production in gliomas seems not related to immune reactions against the tumour and their synthesis by anaplastic astrocytes could follow an unregulated activation of many metabolic processes after neoplastic transformation.