Mixed gliomas (oligo‐astrocytomas) are brain tumours with an admixture of 2 different cell populations: astrocytes and oligodendroglia. On the basis of histological features and behaviour, these tumours are classified as low‐grade mixed gliomas (MG) and malignant mixed gliomas (MMG). We have studied the relationship between c‐myc protein expression and cellular proliferation in this class of tumours. Using antibody c‐33 for c‐myc and PC‐10 for the proliferating cell nuclear antigen (PCNA), immunohistochemistry was performed on 14 MG and 9 MMG. PCNA was increased in MMG as compared to MG in both astrocytic and oligodendroglial areas. However, more c‐myc‐positive cells were seen only in the astrocytic areas of MMG. Analysis of the relationship of c‐myc and PCNA suggests that the correlation of c‐myc with cellular proliferation is dependent on tissue type and differentiation status. © 1996 Wiley‐Liss, Inc.