Regulated Na⁺ absorption maintains a driving force for the continual absorption of fluid from the airspaces of neonatal and adult lungs, and this process is vital for proper lung function. Moreover, this transport of Na⁺ can be acutely regulated via β-adrenoceptors that allow control over the Na⁺ conductance of the apical membrane (G_Na) (Collett et al., 2002) but the signalling pathways that mediate this response have not been fully defined. As β-adrenergic agonists are known to elevate intracellular cyclic adenosine monophosphate (cAMP) levels, it is often assumed that the increase in G_Na must be mediated via protein kinase A. However there is evidence to suggest that the stimulation of Na⁺ transport involves a protein tyrosine kinase (PTK)-dependent pathway (Niisato et al., 1999). In the present study we have therefore explored the effects of the PTK inhibitor tyrphostin A23 (TY23) upon the adrenaline-evoked increase in G_Na.Studies of basolaterally permeabilised cells confirmed (Collett et al., 2002) that isoprenaline normally increases G_Na but this response was abolished by TY23 (Fig 1A). This finding thus accords with data presented by Niisato et al. (1999). Moreover, Western analysis of protein extracted from unstimulated and isoprenaline stimulated cells confirmed that this β-adrenoceptor agonist can increase the abundance of proteins containing phoshorylated tyrosine residues (Fig. 1B). However, this part of the response to isoprenaline was unaffected by TY23 and so the disrupted control over G_Na (Fig 1A) cannot be attributed to an impairment of tyrosine phosphorylation.