Twelve medulloblastomas were screened for their expression of adhesion molecules L1, N.CAM isoforms and HNK1 epitope by Western blotting and immunohistochemistry. Highly sialylated N.CAM isoforms were distinguished from total N.CAMs by using a monoclonal antibody (anti-MenB) specifically recognizing high polymers of 2-8 linked neuraminic acid. All tumors expressed HNK1 epitope, N.CAM and its highly sialylated isoforms on their surface membrane. L1 adhesion molecule was detected by immunohistochemistry in only one medulloblastoma. This spectrum of expression of cell surface adhesion molecules distinguishes medulloblastomas from other primitive neuroectodermal tumors. Medulloblastomas share some immunological features with post-mitotic cells forming the external granular layer of the cerebellum. Western blotting analysis of cerebrospinal fluid (CSF) samples with anti-MenB antibody enabled us to detect highly sialylated N.CAM in some samples. The presence of this antigen in CSF appears to correlate with meningeal spreading of medulloblastomas and could help monitoring chemotherapeutic treatment.