The embryonic Wntβ-catenin ('canonical') pathway has been implicated in epithelial regeneration. To investigate the role of Wnt signal transduction in the airways, I characterised the expression of key pathway components in human bronchial epithelial (HBE) cells and studied the influence of cell density on pathway activity, using subconfluent cells in log-phase growth as a simple model of repairing epithelium. Primary HBE cells and H292 bronchial epithelial cells were found to express TCF-4 and -3, with variable low-level expression of TCF-1 and LEF-1, transcription factors that are regulated by β-catenin. The cells also had the potential to respond to Wnt signals through expression of members of the Frizzled receptor family, including FZD-5 and -6. In confluent H292 cells, 20mM lithium and 25% v/v Wnt-3a conditioned medium induced 4.5-fold (p=O.008) and 1.4-fold (p=O.006) increases in TOPflash activity, respectively. Under conditions of reduced cell density, TOPflash activity increased 1.8-fold (p=O.002) in association with increased nuclear localisation of hypophosphorylated (transcriptionally active) β-catenin and increased cell proliferation. This up-regulation in reporter activity occurred independently of EGF receptor activation and could not be recapitulated by use of low-calcium medium to disrupt cadherin-mediated cell-cell adhesion, but was associated with changes in FZD6 gene expression. I conclude that reactivation of this embryonic pathway might play a role in bronchial epithelial regeneration, and that modulation of Fzd6 receptors may regulate Wnt signalling at confluence. Recognising that chronic inflammatory disorders of the airways involve epithelial damage and repair, I speculate that altered Wnt signalling might contribute to disease pathogenesis or progression.