The effects of treatment with a perfluorochemical emulsion plus carbogen on radiation pneumonitis were examined in a rat model system. Rats received thoracic irradiation (15 Gy) and radiation reactions in the lungs were assessed 25 and 35 days later using bronchoalveolar lavage and histologic assessments. The irradiated lungs showed the expected evidence of acute radiation pneumonitis, including protein leaks and also alveolar infiltrates and interstitial infiltrates. Administration of a perfluoro-chemical emulsion (Fluosol; 15 ml/kg) plus carbogen breathing for 30 min before and during irradiation did not enhance the reactions seen in the irradiated lungs.