A panel of nine monoclonal antibodies raised against human hemopoietic cells was used for immunohistological labeling of frozen sections of human nervous tissues and tumors. Three antibodies showed a remarkably consistent labeling pattern when tested on 18 samples of normal or reactive tissue, on 31 neurogenic and 17 non-neurogenic tumors in an indirect immunofluorescence technique. VIM C6, an antibody recognizing cells of the granulocyte series, showed surface labeling of normal and reactive glial cells and of all types of glioma regardless of the grade of malignancy. VIT 13, an antibody recognizing activated T-cells, labeled the processes of normal, reactive, and neoplastic glia in a manner very similar to but not identical with glial fibrillary acidic protein (GFAP). VIB C5, an antibody recognizing B cells and granulocytes, showed surface labeling restricted to malignant cells (malignant gliomas and primitive neuroectodermal tumors) and fetal brain, thus recognizing, within the nervous system, an oncofetal antigen. Due to this operational specificity within the nervous system, some of the antibodies described here might have a role as diagnostic markers for CNS tumors. This study confirms and expands previous data that sharing of antigenic determinants by hemopoietic cells and nervous tissue or neurogenic tumors is common. However, the significance of such cross-recognition is still obscure. It is tempting to speculate that cross-reacting auto-antibodies might contribute to tissue damage in some immune-mediated neurologic diseases (myasthenia gravis, multiple sclerosis, CNS involvement in systemic lupus erythematosus) or to impairment of immunoregulation in multiple sclerosis or glioma patients. Furthermore, sharing of surface determinants might be responsible for the dual tissue tropism of some viruses, including the lymphotrophic virus (HTLV) in the encephalopathy of the acquired immune deficiency syndrome (AIDS).