Neutrophil (PMN) functions, such as production of toxic oxygen (O2) metabolites, adherence, and chemotactic properties, are modified during local tissue inflammation and sepsis. We hypothesized that PMN would be primed during their transit through injured tissue beds, which in turn can lead to modulation or retention of the primed PMN by downstream tissues like the lungs. We tested this hypothesis by measuring the transpulmonary gradient of hydrogen peroxide (H2O2) production by zymosan-activated PMN. We examined the mixed venous to arterial difference in H2O2(delta H2O2) produced by zymosan-activated PMN in septic patients without lung infiltrates, patients with lung injury, and a control group of patients undergoing elective surgery or coronary catheterization. Septic patients had higher mixed venous H2O2/10(6) PMN, whereas lung injury patients had higher arterial H2O2/10(6) PMN. The control group had the same H2O2/10(6) PMN in mixed venous and arterial blood. The delta H2O2 in septic, lung injury, and control groups were 0.35 +/- 0.22, -0.31 +/- 0.48, and -0.01 +/- 0.04 nmol H2O2/10(6) PMN, respectively. The mixed venous to arterial H2O2 gradient distinguished septic patients from the control and lung injury patients (p less than 0.05). Our results are consistent with the hypothesis that in septic patients PMN are primed in the periphery and downregulated or sequestered in the lung, and in lung injury patients PMN are primed in the lung and sequestered in the periphery. Alternatively, neutrophil-endothelial interactions may downregulate toxic O2 metabolite production by PMN during their transit through microvascular beds.