Polyamine levels have been studied in brain tumor patients. We focused our study on the relationship between tumor, cerebrospinal fluid (CSF) and red blood cell (RBC) polyamine levels. Our results are the following: Polyamine levels in CSF are consistently increased, whatever the histological type may be. The highest tumoral concentrations are found in medulloblastoma. In glioblastomas, the RBC spermidine levels are higher than in the other types of tumors and there is a highly significant correlation between the spermidine/spermine ratio in tumor and RBC. Therefore, RBC polyamine determination might be of clinical interest in the monitoring of patients with glioblastomas.