To investigate the influence of interleukin-1β (IL-1β) on airway epithelial cell growth, we measured [3H]thymidine incorporation and cell numbers of cultured porcine tracheal epithelial cells in the presence or absence of human recombinant IL-1β with or without the following: goat antiporcine polyclonal antibody to platelet-derived growth factor (PDGF); IL- 1 receptor antagonist; indomethacin; PD-145065, a combined endothelin-A and - B receptor antagonist; BQ-123, an antagonist selective for endothelin-A receptors; or phosphoramidon, an inhibitor, in part, of endothelin-converting enzymes, including neutral endopeptidase. We found that IL-1β stimulated the proliferation of airway epithelial cells, and this response was inhibited by the IL-1 receptor antagonist and by PD-145065 or BQ-123. However, neither indomethacin nor PDGF antibody was influential. The endothelin receptor antagonists also decreased basal thymidine incorporation by these cells as did phosphormidon, although to a lesser degree. Data from radioimmunoassays indicated that phosphormidon reduced the endogenous production of endothelin- 1 from the cells, and IL-1β clearly increased it over time. We conclude that IL-1β is a stimulant of airway epithelial cell growth, and its mitogenic effects are mediated, in part, by endogenous endothelin-1 production.