The fetal, normal adult, and malignant squamous epitheliums of the cervix were immunohistochemically examined by the avidin-biotin-peroxidase complex method with monoclonal antibodies for blood group antigens (BGAs) A, B, H, Lewis a, and Lewis b. The results were as follows. 1) ABH antigen compatible with ABO status was found in most normal squamous epithelium of fetal and adult cervix. 2) Compatible ABH and A antigen were abolished in small cell nonkeratinizing squamous cell carcinomas (SNKCs) and large cell nonkeratinizing squamous cell carcinomas (LNKCs), respectively. But no remarkable change in ABH antigen expression was observed in other types of cervical lesions. 3) Precursor H antigen was accumulated in all types of malignant lesions. 4) Incompatible expression of A or B antigen was observed in some cases of LNKCs and keratinizing squamous cell carcinomas. 5) Lewis antigens were abolished to various degrees in malignant lesions of the cervix. The present study showed the change in BGAs expression during carcinogenesis of the cervix, but further investigation is needed to elucidate the interaction between these changes in BGAs and the biological behavior of cancer cells.