Fluosol DA 20% (Fluosol) enhances the response of several rodent tumors to radiation and oxygen. This is a Phase I/II study of Fluosol and oxygen breathing in the radiation treatment of advanced squamous cell carcinoma of the head and neck. Fifteen patients with Stage III/IV tumors entered and completed this trial. Patients received 1.8 Gy/fraction to 45 Gy, at which time the spinal cord was shielded and gross disease was carried to 68-72 Gy. 8 ml/kg (11 patients) or 9 ml/kg (4 patients) Fluosol was infused prior to the first fraction each week for the first 5 weeks. All patients inspired 100% oxygen before and during the initial 25 fractions. The infusions were well-tolerated. Four acute reactions that responded to diphenhydramine or steroids were observed in the 75 infusions. 8/15 patients exhibited liver function abnormalities of 2-3X normal which fell after therapy was discontinued. Normal mucosal reactions were enhanced despite the 1.8 Gy fraction size. 10/15 patients required at least one treatment break: the mean dose achieved before the break was 35 Gy. Tumor clearance was also accelerated. Thirteen patients had primary tumor clearance, but one had a local recurrence. Ten had primary and nodal clearance and 2/3 with nodal persistence had salvage surgery with fibrosis only at pathologic review. One patient, locally controlled, developed distant metastases. Thus, 10/15 patients are NED, but followup time is short.