We have previously demonstrated in primary cancer of the uterine cervix that tumor hypoxia, as determined polarographically, is strongly associated with clinical malignant progression of the disease. Having applied a similar methodological approach to investigate loco-regional relapses, we found a pronounced shift to more hypoxic oxygenation profiles in the recurrent tumors than in the primary tumors. Median pO2 values in 53 pelvic recurrences were significantly lower than the median pO2 values of 117 primary tumors of comparable sizes (7.1 +/- 1.1 mmHg vs. 12.1 +/- 1.0 mmHg, p = 0.0013). The differences in tumor oxygenation between primary and recurrent tumors mirrored the differences in the patients' 5-year survival probabilities. In the cohort of patients with pelvic relapses, median tumor pO2 < 4 mmHg indicated a significantly shorter median survival time as compared to median tumor pO2 > or = 4 mmHg. Our results further support our thesis that in cervical cancer, tumor hypoxia and clinical aggressiveness in terms of resistance to therapy and tumor dissemination, are interrelated.