PET studies with 2-18F-fluorodeoxyglucose (FDG) were carried out in 15 patients with bronchial carcinomas, first under fasting conditions and then 2 days later during intravenous infusion of a 20% glucose solution which raised the plasma glucose level from 84.6 +/- 14.7 to 168.3 +/- 23.6 mg/100 ml (n = 15, p < 0.001). Tumor metabolism was quantified by the dose absorption ratio (DAR) of FDG uptake [DAR = tissue concentration/(injected dose/body weight)] and also by the rate of glucose consumption (MR) as measured by the Patlak graphical approach in 12 patients. The DAR decreased from 5.07 +/- 1.89 under fasting conditions to 2.84 +/- 0.97 (-41.8% +/- 15%, n = 15, p < 0.001) during glucose infusion, while the MR remained constant (4.71 +/- 2.38 mg/100 ml/min versus 4.96 +/- 2.46 mg/100 ml/min, n = 12, ns). Correction of the DAR data by plasma glucose level eliminated the significant difference between the fasting and glucose load [4.24 +/- 1.59 versus 4.70 +/- 1.45 (n = 15, ns)], but considerable changes in individual patients remained. These data indicate that the DAR of FDG uptake in bronchial carcinomas is influenced significantly by plasma glucose levels. Dynamic quantification of glucose metabolism using the Patlak approach is less dependent on the plasma glucose level and appears advantageous when high reproducibility is needed.