Thioredoxin Reductase (TrxR) is a key enzyme in reactive oxygen species (ROS) detoxification and in redox regulation. Because cancer cells produce increased steady-state levels of ROS (i.e., superoxide and hydrogen peroxide), TrxR is viable target in clinical trials using the anti-rheumatic drug, auranofin (AF). To extend these observations to small cell lung cancer (SCLC), AF-mediated TrxR inhibition as well as tolerability and tumor growth inhibition was determined in a xenograft model. AF was administered intraperitoneal, daily or twice daily for 1 to 5 days in mice bearing DMS273 xenografts. AF uptake was determined by mass spectrometry of gold and inhibition of TrxR in the tumor was determined. The optimal dose was 4 mg/kg once daily resulting in 18 μM gold in the plasma and 50% inhibition of TrxR activity in DMS273 SCLC tumors. This regimen given for 14 days provided a trend for prolonged median survival from 17.5 to 22 days (p=0.058, N=20 controls, 19 AF) without causing changes in bodyweight, bone marrow toxicity, blood urea nitrogen or creatinine. These results support the hypothesis that AF is an effective inhibitor of TrxR and suggest that AF could be used as an adjuvant in radio-chemotherapy protocols to enhance therapeutic efficacy.