The results of immunohistochemical detection of p53 protein in a large variety of CNS neoplasms with the polyclonal antiserum CM1 are presented. Immunoreactivity in at least several cells were regularly found in astrocytic neoplasms including glioblastomas; it was also frequent in medulloblastomas and oligodendrogliomas and could be found in more than 50% of acoustic schwannomas and esthesioneuroblastomas. Meningiomas also showed several immunoreactive cells in about 40% of the cases. Certain neuronal/neuronal-glial tumours (such as central neurocytomas, dysembryoplastic neuroepithelial tumours, gangliocytomas, dysplastic gangliocytomas of the cerebellum etc.) were consistently negative, whereas gangliogliomas (with the exception of the regularly positive desmoplastic gangliogliomas) very rarely displayed immunoreactive glial cells. Positive findings, however, seem to be more frequent in anaplastic gangliogliomas where they may be of prognostic significance. The same may be valid in ependymomas. The underlying mechanism for p53 immunopositivity, however, can be very heterogeneous and possibly even contrary (either accumulation of inactive mutant protein or detection of active wild-type protein), therefore isolated immunohistochemical findings call for very cautious interpretation.