The expression of mucin genes in the normal glandular epithelium of the endocervix has been well characterized. However, mucin gene expression in neoplastic or particular non-neoplastic glandular cervical lesions has not been addressed. This immunohistochemical study was carried out to analyze the expression of MUC2 and MUC5AC in neoplastic and non-neoplastic glandular lesions of the cervix. Monoclonal antibodies were used on paraffin-embedded sections from 41 adenocarcinomas, 2 adenosquamous carcinomas, 13 adenocarcinomas in situ (ACIS), 3 glandular dysplasias, 8 endometrioses, 5 tubal metaplasias, 17 squamous metaplasias, 3 microglandular hyperplasias and normal tissue of the endocervix, endometrium and fallopian tube. The patterns of expression of MUC2 and MUC5AC were different and in principle contrary. Focal MUC2 expression was observed almost exclusively in neoplastic lesions (36%) and not in normal epithelia and non-neoplastic lesions, the one notable exception being immature metaplasia. In contrast, strong expression of MUC5AC was observed in both normal endocervical epithelium (100%) and neoplastic lesions (73%). The expression of MUC5AC, however, was diminished in most neoplastic glandular lesions. Co-expression of MUC2 and MUC5AC was consistently documented in the lesions with intestinal differentiation. In contrast, cases of tubal metaplasia and endometriosis were negative for MUC2 and MUC5AC. These results indicate that discrimination of mucin gene expression may be helpful in discriminating lesions of the cervix.