The monoclonal antibody Myc 1-6E10 was used in an immunocytochemical technique to examine the expression of the c-myc oncogene in normal endocervices and those with glandular intraepithelial neoplasia and invasive malignancy. Eleven of 14 normal endocervical biopsy specimens did not express the gene, while three showed nuclear, or light basal cytoplasmic localisation of the gene product, or both. All but one of 14 cases of low and high grade glandular intraepithelial neoplasia, and all 17 cases of invasive adenocarcinoma, showed a pan-cellular pattern of immunostaining. Of considerable additional interest was the demonstration of field changes in morphologically normal glandular epithelium in those biopsy specimens with concurrent cervical glandular intraepithelial neoplasia or adenocarcinoma. This was manifest as increased concentrations of myc proteins compared with normal tissues. These results further support the role of the c-myc gene in oncogenesis, and in the light of field changes, suggest possible difficulties in the clinical management of this group of patients.