This study demonstrates by an updated analysis of an ongoing prospective study that tumor oxygenation, as measured with a validated standardized polarographic needle electrode method before treatment, powerfully predicts the prognosis of patients receiving radiotherapy for intermediate and advanced stage cancer of the uterine cervix. First evidence for a host component in tumor oxygenation based on a significant correlation between median pO(2) values determined in normal subcutaneous fatty tissue and in cervical cancer is also presented. Further investigations are necessary to clarify whether tumor hypoxia is just a marker of intrinsic tumor aggressiveness or whether the negative impact of tumor hypoxia on survival is related to radiobiological mechanisms caused by hypoxia per se, which may include (1) the reduced oxygen enhancement effect, (2) increased radioresistance due to expression of genes for cell cycle delay and stress proteins, and/or (3) accelerated tumor progression to more radioresistant and metastatic variants by increased genetic heterogeneity.