Work in swine confinement buildings leads to an inflammatory response and may be associated with increased levels of acute phase proteins. We compared the inflammatory response of a control group of young former farm workers with agematched former farm workers who had previously developed the lower airway symptoms of wheeze, cough, tightness of the chest during work in swine confinement buildings, and because of these symptoms had stopped work. Both groups were subjected to an experimental exposure in a swine confinement building for 3 hours. Complement activation and acute phase proteins were measured in blood samples and broncho-alveolar lavage. Plasma C3d levels correlated with respirable dust, significantly so for individual FDVHV_ DQG_ IRU_ WKH_ ZKROH_ FRKRUW__ 3ODVPD_ &___ ILEULQRJHQ_ DQG_ .1-acid glycoprotein peaked 1 and 6 h after exposure start, mannan-binding lectin, C-reactive protein DQG_.1-antitrypsin peaked after 2 h. Surfactant protein D (SP-'__DQG_.2-macroglobulin were downregulated. In lavage, only SP-'__ .2-macroglobulin and fibronectin were detected. FEV1, FVC, TLC and FEV25-75 did not vary during exposure. There was complement activation in response to respiratory dust, more so amongst cases than in the control group. Acute exposure, with work related levels of organic dus containing endotoxin, leads to a weak systemic inflammatory response