Malignant neoplasms commonly have increased rates of glucose utilization, poor perfusion and areas of low oxygenation. Autoradiographic studies of excised tumors have shown increased FDG uptake in viable cells near necrotic portions of tumor. We evaluated in vitro whether tumor cell FDG uptake increased with hypoxia. METHODS The uptake of 3H-FDG into two human tumor cell lines (HTB 63 melanoma and HTB 77 IP3 ovarian carcinoma) was determined after exposure to differing oxygen atmospheres ranging from 0% to 20% O2 for varying time periods. Glucose transport was independently determined as well as estimates of the level of Glut-1 glucose transporter membrane protein. RESULTS FDG uptake in both the melanoma and the ovarian carcinoma cell lines increased significantly (39.6% +/- 6.7% and 36.7% +/- 9%, respectively) over basal (20% O2) conditions when cells were exposed to a mild hypoxic environment (5% O2) for 1.5 hr. With a 4-hr exposure to 1.5% O2, the increase in FDG uptake was greater at 52.3% +/- 8.9% and 43.5% +/- 19%, respectively. With 4 hr of anoxia, the increase in FDG uptake over basal conditions was 42.7% +/- 10% and 63.3% +/- 13.7% for melanoma and ovarian carcinoma cells, respectively. Membrane transport of 3-O-methylglucose (3-OMG) was increased by hypoxia for melanoma and ovarian carcinoma. Immunochemical assays for Glut-1 showed an increase in the membrane expression of the Glut-1 transporter in cells exposed to hypoxia. CONCLUSIONS Hypoxia increases cellular uptake of FDG in two different malignant human cell lines. Increased glucose transport, in part due to increased membrane expression of the Glut-1 glucose transporter, contributes to this phenomenon. Increased FDG uptake in tumors visualized during PET imaging may be partly reflective of tumor hypoxia.