We have localized the mRNA of the epidermal growth factor receptor (EGF-receptor) in nuclei of A431 cells by non-radioactive in situ hybridization at the light microscopical level using digoxigenin-labelled DNA probes. Both formaldehyde and glutaraldehyde fixations were tested before the hybridization was performed. Glutaraldehyde, compared with formaldehyde fixation, gives a less diffuse hybridization signal, which is easier to localize. Therefore, glutaraldehyde was used as a fixative in the hybridization experiments. It is demonstrated that the mRNA of the EGF-receptor is present in restricted domains mainly located around the nucleolus. This location of the EGF-receptor mRNA was unaltered after extraction of chromatin. Therefore it is concluded that the messenger RNA of the EGF-receptor is attached to the nuclear matrix. A possible biological role for the location of mRNA of the EGF-receptor around the nucleolus is discussed.