OBJECTIVE To investigate whether electrode measurements of tumor oxygenation obtained under a range of different treatment conditions designed to alter the degree of tumor hypoxia could be correlated with estimates of radiobiological hypoxia measured under the same conditions. METHODS Experiments were performed in restrained, nonanesthetized, female C3H/He mice, which had approximately 0.5 g KHT sarcomas growing intramuscularly in the hind limbs. The treatments used to modify tumor oxygenation status included breathing gas mixtures of varying oxygen content, altering tumor blood flow, and shifting the hemoglobin oxygen dissociation curve. Radiobiological hypoxic fraction was estimated using the paired survival curve assay, while electrode measurements of tumor oxygenation were obtained with an Eppendorf histograph. RESULTS With the selected manipulations it was possible to vary the radiobiological hypoxic fraction in the tumors from approximately 1 to approximately 100% of the total viable cell population. Furthermore, these changes in radiation response were directly reflected in the changes in tumor oxygenation measurements made with the Eppendorf histograph. CONCLUSIONS These findings suggest that in the KHT tumor model the Eppendorf electrode measurements could predict the response of the tumors to radiation as determined by the proportion of hypoxic cells.