We studied 23 cases of capillary hemangioblastoma (CHB) of the cerebellum with 17 immunohistochemical cell markers in an attempt to define the nature of the so-called "stromal" cells. These cases were compared to four cases of intracranial metastatic renal cell carcinoma (RCC), which may mimic CHB histologically. The 17 markers studied included vimentin (VIM), Factor VIII-related antigen (FVIIIR:Ag), blood group antigens A, B, and H, Ulex I lectin (Ulex), Alkaline Phosphatase (Alk P), neurofilament protein (NF), glial fibrillary acidic protein (GFAP), S-100 protein (S-100), nerve growth factor receptor (NGFR), muscle-specific actin (MSA), desmin (Des), monoclonal keratin (MKER, including Cam 5.2 and AE1/3), epithelial membrane antigen (EMA), and chromogranin (Chrom). No significant stromal cell staining was seen by markers for endothelial, epithelial, chromaffin, or smooth muscle origin. In some cases individual cells demonstrated positivity for GFAP (4/22) and S-100 protein (13/23); these cells were generally stellate and located near the periphery, and we conclude that these were the result of entrapment of surrounding cerebellum. No case demonstrated NF in stromal cells. However, nearly all cases of CHB showed stromal cell staining with VIM (19/22). In contrast, all of the cases of RCC showed significant staining for at least one marker of epithelial origin (3/4 for MKER and 4/4 for EMA). We conclude that the stromal cell of CHB is neither endothelial, neural, epithelial, pericytic, nor neuroendocrine in origin, and is instead of undifferentiated mesenchymal origin. The designation of this tumor as an "hemangioblastoma," although a misnomer, is firmly established in the literature and should probably be retained.