Myofibroblasts have been previously described beneath the bronchial epithelium and were found to increase in number proportional to the accumulation of extracellular matrix in the bronchial lamina reticularis in asthma. The aim of this study was to assess further the contribution of these structural cells to allergic inflammation in the bronchial mucosa through their cytokine expression. Cell cultures were established from the lamina reticularis of human bronchial biopsies from asthmatic and non-asthmatic subjects. Cytokine secretion was measured by ELISA in supernatants of cultures with or without tumour necrosis factor-alpha (TNF-alpha). The mRNA levels for granulocyte-macrophage colony-stimulating factor (GM-CSF) in the cultures were examined by ribonuclease protection assays (RPAs). Bronchial myofibroblasts grown from bronchial biopsies were capable of producing GM-CSF, interleukin-6 (IL-6), interleukin-8 (IL-8), and stem cell factor (SCF) constitutively. The GM-CSF production by myofibroblasts was significantly increased in response to TNF-alpha simulation with a corresponding increase in GM-CSF mRNA expression. The enhancement of GM-CSF production by TNF-alpha in myofibroblasts was blocked by the inhibition of RNA synthesis. Prednisolone abolished the GM-CSF production. This study provides evidence for the role of bronchial myofibroblasts in the regulation of inflammatory cell recruitment and activation by interaction in the cytokine network in the bronchial mucosa.