To compare the Ki-67 and Proliferating Cell Nuclear Antigen (PCNA), markers of cell proliferation, paraffin embedded surgical specimens from 56 human astrocytic tumours (8 pilocytic tumours, grade I; 9 low (II) grade and 9 anaplastic (grade III) astrocytomas and 30 glioblastomas, grade IV) were immunolabelled with the anti-PCNA (PC 10, DAKO) and anti-Ki-67 (DAKO) antibodies. For the latter immunostaining the microwave oven processing was performed. The Ki-67 and PCNA labelling indices (LIs) were statistically compared. For the majority of cases, PCNA LI was higher than that obtained with anti-Ki-67 antibody and the intensity of staining for PCNA was more variable. The statistically significant difference of the percentage of PCNA LIs was found only between low grade (I and II) and high grade (III and IV) tumours, while Ki-67 LIs discriminates each group of glial tumours; thus this latter marker is more sensitive and specific.