Bacterial lipopolysaccharides (LPS) are potent inducers of pro-inflammatory cytokines via activation of nuclear factor– kappa B (NF–κB) and mitogen activated protein kinase (MAPK) signalling pathways [1]. Bacterial infections also modify the ion transport processes that control lung fluid homeostasis and this may contribute to the formation of pulmonary oedema [2]. Therefore, we investigated the effect of LPS on expression of the pore-forming α–subunit of the amiloride-sensitive Na⁺ channel (ENaC) and amiloride-sensitive Na⁺ transport across H441 human lung epithelial cells. We have used inhibitors of NF–κB and MAPK activation to examine the role of these signalling pathways in LPS mediated effects. H441 cells were cultured at air interface on permeable supports for 7 days, mounted in Ussing chambers and bathed in physiological saline. H441 monolayers exhibited a mean resistance (R_t) of 240± 50 Ω.cm^-2 Spontaneous short circuit current (I_sc) was measured by clamping transepithelial voltage (V_t) at zero. Amiloride-sensitive I_sc was calculated after application of 10μM amiloride to the apical chamber (IC₅₀ = 0.9μM). As spontaneous I_sc varied between batches of cells, treatments were carried out on paired monolayers from the same batch of cells and results analysed using Student’s paired t–tests. Data are presented as mean±SEM. Incubation of cells for 16 hours with 15μg.ml^-1 LPS (from Ps. aeruginosa) caused a significant reduction in amiloride-sensitive I_sc from 14 ± 2 to 7 ± 2 μA.cm^-2, p=0.01, n=6). There was no change in amiloride-insensitive I_sc or resistance of the monolayers. The LPS-induced reduction in I_sc was associated with a decrease in αENaC mRNA and protein abundance. Treatment of cells with 5mM sulphasalazine (SAS), an inhibitor of NF–κB activation, or 25 μM caffeic acid (CAPE), an inhibitor of NF–κB nuclear translocation, prior to addition of LPS did not restore amiloride-sensitive I_sc to control levels. However, pre-treatment with 20μM PD98059 (to inhibit MAPK activity) resulted in an increase in amiloride-sensitive I_sc that was significantly higher than cells treated with LPS alone (26 ± 3.0 μA.cm^-2, 13 ± 5.0 μA.cm^-2 respectively, p〈0.05 n=4). Furthermore, αENaC protein levels were more abundant in these cells compared to those treated with LPS alone. Our data indicate that LPS decreases amiloride-sensitive Na⁺ transport across H441 human lung epithelial cells by reducing αENaC abundance and that this effect is mediated by a pathway that involves activation of MAPK.