We determined changes in vascular resistance and microvascular permeability during anaphylactic reaction in isolated canine lungs perfused at constant pressure with autologous blood. In lungs with anaphylaxis induced by an intra-arterial injection of Ascaris suum antigen (10 mg), pulmonary vascular resistance and capillary pressure assessed as double occlusion pressure increased transiently by 10 times and 6.3 mmHg, respectively. Pre- to postcapillary vascular resistance ratio decreased from 0.89 +/- 0.05 to 0.21 +/- 0.06, suggesting predominant pulmonary venoconstriction. In lungs perfused in the antidromic direction from the pulmonary vein to the artery, anaphylaxis caused marked precapillary vasoconstriction, consistent with pulmonary venoconstriction. Vascular permeability assessed using the capillary filtration coefficient and isogravimetric capillary pressure did not change significantly for 3 h in either group. No changes were found in any variables in the saline-injected control lungs. The final weight of the anaphylactic lungs was significantly greater than that of the control lungs. Thus we conclude that anaphylaxis in isolated canine lung produces an increase in capillary pressure due to pulmonary venoconstriction without significant changes in vascular permeability. Pulmonary edema accompanied by anaphylactic hypotension may result from an increase in pulmonary hydrostatic intravascular pressure but not an increase in pulmonary vascular permeability.