The purpose of the present study was to identify cytokeratin polypeptides that are specifically associated with the basal and luminal epithelia of the human prostate. This aim was accomplished by immunohistochemical and immunoblot analysis of human prostate using cytokeratin-specific monoclonal antibodies. In immunohistochemical studies, monoclonal anticytokeratin 8.12 exhibited immunoreactivity with the basal, but not luminal, epithelial cells of fetal, juvenile, normal adult, and hyperplastic prostate. The 8.12 antibody did not stain prostate cancer tissues. Epithelia of 30 and 36 week fetal prostate contained only basal cells whereas both luminal and basal cells were noted in 7 month and 1 year old juvenile prostate. This finding suggests a stem cell function for the prostatic basal cells. Immunoblot analysis of proteins separated by two-dimensional electrophoresis showed that cytokeratins 5 and 15 were basal-cell-specific cytokeratins that were absent from prostatic carcinoma while cytokeratins 8 and 18 appear to be luminal-cell-specific. These results indicate that antibodies to specific cytokeratin polypeptides can be used not only to differentiate between prostatic basal and luminal cells but also to study the biological processes of prostatic organogenesis and carcinogenesis.