A monoclonal antibody, MIB1, recognizes Ki-67 antigen in routinely processed paraffin sections after microwave treatment. Cycling cells are positive for MIB1, and quiescent cells are negative for MIB1. MIB1 index represents the growth fraction of the cell population. Cervical biopsies taken from 186 patients with stage III squamous cell carcinoma prior to radiotherapy were investigated for MIB1 reactivity using an immunohistochemical method. Cancer cells that were positive for MIB1 showed an intranuclear or chromosomal positive pattern. The median MIB1 index was 43% (range, 18-74%). Of 186 patients, 87 had a MIB1 index of > 43% and the other 99 had an index of < 43%. The 5-year survival rates were 58% (50 of 87 patients) in the former group and 58% (57 of 99 patients) in the latter group. The chi 2 test indicated that no significant prognostic correlation existed between two groups (p = 0.989). We conclude that the MIB1 index demonstrates a considerable variation among patients and is not a predictive indicator of survival for patients with stage III cervical squamous cell carcinoma.