Technical Abstract: Previously we reported that intratracheal administration of lipopolysaccharide (LPS) elicits pulmonary hypertension (PH) in broilers reared under commercial conditions, in broilers reared in environmental chambers and pre-treated with aerosolized red food colorant # 3 and propylene glycol (Red#3+PG), but not in control broilers reared in environmental chambers. The objective of the present experiment was to determine possible changes in the number or proportion of airway leukocytes that could contribute to the magnitude of the PH responses elicited in broilers. Birds were aerosolized for 40 min with a saturated mixture of Red#3+PG. After 24 h a blood sample was taken, the broilers were euthanized, and a pulmonary lavage process was conducted in each bird. Leukocyte concentration (WBC/micro L) and differential leukocyte counts (%) were measured in blood and lavage fluid. Leukocyte concentration in blood did not differ between groups but the percentage of blood lymphocytes was lower in broilers from the Red#3+PG group compared to birds from the control group. Cells recovered from the lavage fluid from both groups were primarily heterophils. The concentration of leukocytes was higher in the lavage fluid of broilers from the Red#3+PG group compared with broilers from the control group but the proportions among leukocytes were not different between the two groups. We propose that the increased concentration of leukocytes present within the airways is one of the components that enable broilers pre-treated with aerosolized Red#3+PG to exhibit PH responses to intratracheal LPS.