To clarify the role of polymorphonuclear leucocytes (PMNs) in acute lung injury, acute experimental lung injury was produced by intravenous injection of endotoxin to male Hartley guinea pigs. White blood cell (WBC) counts in the peripheral blood, total nucleated cell counts and PMNs' population in the lung lavage fluid, chemotaxis and chemiluminescence of the PMNs in the blood and in the lung lavage fluid were studied. Results were as following 1. WBC counts in the blood decreased after injection of endotoxin. In the lung lavage fluid, total nucleated cell counts and the differential counts of PMNs increased with time. 2. The chemotaxis of PMNs in the blood decreased significantly (647 +/- 118 cells/5 high-power-fields (5HPF) in no treatment group (NT group), vs 256 +/- 120 cells/5HPF in 6 hours after endotoxin injection group (6h group), p less than 0.01), but that in the lung lavage fluid increased significantly (93 +/- 63 cells/5HPF in NT group, vs 334 +/- 24 cells/5HPF in 6h group p less than 0.01). 3. The chemiluminescence of the PMNs in the blood increased (3.64 +/- 2.41 counts/cell in NT group, vs 51.2 +/- 32.9 counts/cell in 6h group, p less than 0.01), and that in the lung lavage fluid increased (1.89 +/- 0.94 counts/cell NT group, vs 59.2 +/- 49.1 counts/cell in 6h group, p less than 0.01). We concluded that increased chemotaxis of PMNs contributed to the influx of PMNs into the alveolar spaces after endotoxin injection. As the pMNs in the alveolar spaces had increased ability to produce active oxygen metabolite, they might be involved in the progression of endotoxin-induced acute lung injury.