Recent studies indicate that a focal, limited, inflammatory response can be safely elicited after direct bronchial instillation of small doses of endotoxin into a single lung segment. Since the radiotracer [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) is taken up at accelerated rates within inflamed tissues, we hypothesized that we could detect and quantify this regional inflammatory response with positron emission tomography (PET). We imaged 18 normal volunteers in a dose escalation study with 3 endotoxin dosing groups (n=6 in each group): 1 ng/kg, 2 ng/kg, and 4 ng/kg. Endotoxin was instilled by bronchoscopy into a segment of the right middle lobe, with imaging performed ~24 hr later, followed by bronchoalveolar lavage (BAL). A "subtraction image analysis" was performed in the highest dose cohort to identify the area of inflammation, using the pre-endotoxin scan as a baseline. BAL neutrophil counts were significantly higher in the highest dose group compared to the other two groups (1413±625 vs 511±396 and 395±400 cells/mm³, p<0.05). Autoradiography performed on cells harvested by BAL showed specific [³H]deoxyglucose ([³H]DG) uptake limited to neutrophils. In vitro [³H]DG uptake in BAL neutrophils in the 4 ng/kg dose group (but not in the 2 ng/kg dose group) was statistically greater than in peripheral blood neutrophils obtained before or after endotoxin instillation. The rate of [¹⁸F]FDG uptake was greatest in the 4 ng/kg group, with a consistent, statistically significant increase in the rate of uptake after endotoxin instillation compared to baseline. We conclude that the inflammatory response to low dose endotoxin in a single lung segment can be visualized and quantified by imaging with FDG-PET.