Cultured neuroblastoma cells and neuroblastoma-glioma cells have been shown to contain renin activity, angiotensin-converting enzyme activity, and angiotensins. It has been assumed that these cells also produce angiotensinogen as the substrate of an intracellular renin-angiotensin system. However, measurements of angiotensinogen have not been reported in the neuroblastoma or neuroblastoma-glioma cells, and the possibility that the cells generate angiotensins from fetal bovine angiotensinogen has not been eliminated. In this work angiotensinogen was shown to accumulate in the serum-free medium of thoroughly washed neuroblastoma cells (mouse Neuro-2A and rat B103) and glioma cells (rat C6). Separate experiments demonstrated that mouse Neuro-2A cells continue to produce angiotensinogen even after two passages in a defined serum-free culture medium. Further evidence that the angiotensinogen was not a contaminant from fetal bovine serum was obtained by the use of a monoclonal antibody raised against angiotensinogen of rat plasma. The angiotensinogen of Neuro-2A and C6-glioma cells is bound by the monoclonal antibody, whereas fetal bovine angiotensinogen is not bound. These results are consistent with the hypothesis that angiotensinogen is produced locally in the brain and in neuroblastoma cells as a substrate for an intracellular renin-angiotensin system.