Recent clinical studies suggest that the degree of tumor oxygenation may be predictive of the response of radiation therapy for cancer. In an exploratory investigation of cervical lymph node metastases in 27 patients with advanced squamous cell carcinoma of the oropharynx and hypopharynx, this relationship was investigated by means of oxygen measurements with an Eppendorf PO (2) histograph. The measurements were made before the start of radiation therapy and after the first week of therapy. Clinical response was evaluated 6 weeks after the completion of therapy. Before therapy, marked hypoxia was observed in the lymph node metastases, with a mean PO (2) value of 16.1 +/- 8.2 mm Hg and a hypoxic fraction (PO (2) < 10 mm Hg) of 56.4% +/- 20.0%. After the first week of radiation (9 Gy) there was a general reoxygenation (DeltaPO (2) = 5.0 +/- 10.1 mm Hg, P < 0.05; Deltahypoxic fraction = -11.3% +/- 31.3%, P = 0.11). A relationship between the degree of reoxygenation and tumor response was not observed. Patients without at least partial lymph node response (n = 8) showed poorer pretherapeutic oxygenation (PO (2) mean = 11.1 +/- 2.9 mm Hg) than those who responded to the therapy (n = 19, PO (2) mean = 18.2 +/- 8.8 mm Hg). In this investigation of a defined set of patients with advanced carcinoma of the oropharynx and hypopharynx, we found that pretherapeutic oxygenation data are predictive for the therapeutic response to radiation therapy or radiochemotherapy.