Studies of fetal lambs have shown that thyroidectomy abolishes the adrenaline-evoked absorption of lung liquid that is normally seen during labour and birth. However, whilst this effect can be reversed by exogenous T₃,delivering T₃ to immature fetuses does not cause precocious absorption of lung liquid unless it is given with a glucocorticoid (Barker et al., 1991). As this absorptive process is driven by active Na transport (Olver et al., 2004), it thus appears that thyroid and glucocorticoid hormones are both important to the initiation and maintenance of the adult lungs’ absorptive phenotype.Our earlier work shows that H441 distal airway epithelial cells do not transport Na if maintained in the absence of such hormones, but that 0.2 µM dexamethasone, a synthetic glucocorticoid, stimulates electrogenic Na transport by evoking expression of a selective apical Na conductance (Ramminger et al., 2003). The present study therefore explored the possibility that T₃ may also play a role in this process and our data (Fig 1) show clearly that T₃ potentiates the dexamethasone-induced increase in G_Na.T₃ thus appear to be involved in the control of epithelial Na absorption (see also Pachá et al., 1996), which may explain the abnormally high incidence of respiratory distress amongst congenitally hypothyroid infants (Cuestas et al., 1976).