To investigate whether blood components, such as complements, antibody, platelets and leukocytes, can play important roles in increasing pulmonary arterial and airway pressures after antigen challenge in sensitized rabbits, we measured the time course of pulmonary arterial pressure, airway pressure and lung weight gain after antigen challenge in isolated perfused rabbit lungs. Nineteen rabbits were divided into 3 groups; S group (n = 9), which was sensitized rabbit lung with antigen added into perfusate; NS group (n = 5), which was nonsensitized rabbit lung with antigen added into perfusate; S+R group (n = 5), which was sensitized rabbit lung with autologous erythrocytes added into perfusate. Although agglutinin titer in sensitized rabbits was more than 1: 10,000, that in the perfusate was less than 1:16. Pulmonary arterial and airway pressures significantly increased after antigen challenge in S group, while those in NS and S+R groups did not show any change. Also there were no significant changes in pulmonary arterial and airway pressures and lung weight gain in nonsensitized rabbit lungs of the same agglutinin titer as S group. Lung weight gain in S group was 2-4 times higher than that in S+R group after antigen challenge. We conclude that blood components, such as complements, antibody, platelets and leukocytes, do not play important roles on antigen induced pulmonary responses in sensitized rabbit lungs.