Role of sympathetic nerves in increasing the lung vascular permeability was investigated in the presence of papaverine using an isolated rat lung perfusion preparation. Sympathetic nerve stimulation was performed at different time points before and after pressure-induced weight gain. When stimulated at 3 or 7 min after the pressure associated increment, stimulation evoked a further increase in lung weight, particularly in the former case. In contrast, stimulation performed before or 15 min after the pressure increment elicited no such response. The histological finding of carbon particles in the perivascular wall after sympathetic nerve stimulation also provided direct evidence of increased lung vascular permeability.