This study examines the changes in tumor pO2 distribution assessed by polarography (KIMOC 6650, Eppendorf) in 1) two human tumor xenografts after carbogen inhalation with or without a perflubron (perfluorooctylbromide) emulsion (Oxygent, Alliance Pharmaceutical corp.) and in 2) human head and neck carcinomas after carbogen inhalation. Mice bearing HRT18 or NA11+ tumors were restrained and their body temperature was kept constant. Perflubron emulsion (4 ml/kg) was injected i.v. in the mice. In patients, oxygenation of the head and neck metastatic lymph nodes was assessed before and/or during carbogen exposure. The distribution of pO2 values shifted upwards during carbogen exposure in both animals and patients while the proportion of low pO2 values decreased. The maximal effect was obtained with patients after 1 to 6 minutes of carbogen exposure, but 4 patients still maintained very low pO2s. Carbogen plus 4 ml/kg perflubron emulsion was more efficient than carbogen alone for increasing hypoxic tumor pO2 in animals. If the animals data could be extrapolated to humans, then the effect of carbogen on tumor oxygenation should be increased by perflubron emulsion administration.