An immunohistochemical study was performed on the paraffin sections of 25 tumors in the central nervous system (CNS) with prominent papillary configurations. These tumors included seven metastatic papillary carcinomas, six choroid plexus tumors, four papillary ependymomas, two myxopapillary ependymomas, two papillary pituitary adenomas, two astroblastomas, one papillary meningioma, and one anaplastic astrocytoma with significant papillary changes. The panel of antibodies applied included anti-glial fibrillary acidic protein (GFAP), anti-carcinoembryonic antigen (CEA), anti-vimentin (VM), anti-S-100 protein (S-100 P), anti-cytokeratin, and anti-prealbumin antisera. All ependymomas and astroblastomas examined expressed both VM and GFAP, which were either absent or focally expressed in choroid plexus tumors. In contrast, all choroid plexus tumors showed anti-cytokeratin immunoreactivity that was absent in the ependymomas and astroblastomas. Five choroid plexus tumors also expressed S-100 P, thus differentiating them from metastatic carcinoma that showed negative immunostaining. Anti-CEA antisera immunoreactivity was seen in six metastatic tumors, whereas none of the primary CNS tumors expressed CEA. Prealbumin was expressed in four choroid plexus tumors and two metastatic tumors. Immunohistochemical typing using a panel of antibodies has allowed the differentiation of most of the papillary tumors in the CNS examined in this study.