Data are presented on p53 protein presence in human oligodendrogliomas whose progress from low grade to anaplastic oligodendroglioma can be followed. Expression was evaluated by formalin-fixed paraffin-embedded section immunohistochemistry, using monoclonal PAb 1801 antibody. The frequency of p53 protein accumulation is related to the stage of tumor malignancy. All the samples (100%) of malignant oligodendrogliomas were positive for p53 protein. Of 14 type II oligodendroglioma samples, 9 were positive (64%) while among type I oligodendroglioma the positivity was 28%. The mean proportion of reactive cells was also higher in malignant oligodendrogliomas. However, mean intensity staining did not differ among various grades of tumors. Our results point to the direct link between p53 protein accumulation and the malignant stage of human oligodendrogliomas. However, the value of p53 protein accumulation in predicting malignant behavior of oligodendrogliomas requires further confirmation.