Exposure to swine dust causes airway inflammation with increased levels of proinflammatory cytokines, and inflammatory cells in nasal and bronchoalveolar lavage fluid (BALF) in healthy subjects. Earlier studies have suggested that lipopolysaccharides (LPS) might be an important proinflammatory factor in swine dust. Since respiratory epithelial cells and alveolar macrophages are target cells for the inhaled dust, we therefore compared the release of proinflammatory cytokines from normal human bronchial epithelial cells (NHBE), an epithelial cell line (A549) and from human alveolar macrophages obtained from BALF from healthy subjects in vitro after incubation with dust collected in swine houses or LPS. Swine dust or LPS was added to the wells with A549 cells or macrophages and incubated for 8 h at concentrations of 12.5, 25, 50 and 100 microg/ml. NHBE cells were incubated with swine dust at a concentration of 25, 50 or 100 microg/ml or with LPS at a concentration of 50 or 100 microg/ml and incubated for 24 h. The supernatants were collected, centrifuged, and IL-6, IL-1beta and tumour necrosis factor-alpha (TNF-alpha) production was measured using an ELISA method and expressed per 106 cells. Swine dust and LPS caused a dose-dependent increase of IL-6 production in NHBE cells, swine dust being more potent than LPS. In A549 cells, only swine dust, but not LPS caused an increase of IL-6 production. Neither swine dust nor LPS induced IL-1beta or TNF-alpha release from A549 cells. Both swine dust and LPS caused a dose-dependent increase of IL-1beta, IL-6 and TNF-alpha in alveolar macrophages. Swine dust which contained 2.2 (0.2) ng endotoxin/100 microg swine dust (0.02 per thousand) was almost as potent as LPS in inducing cytokine release from alveolar macrophages in vitro. We conclude that both epithelial cells and alveolar macrophages have the capability to contribute to the release of proinflammatory cytokines following exposure to swine dust. Some agent(s) other than LPS in the dust contribute to the marked airway inflammatory reaction.