Roflumilast is an orally active phosphodiesterase 4 (PDE4) inhibitor approved for use in chronic obstructive pulmonary disease. Roflumilast N-oxide (RNO) is the active metabolite of roflumilast and has demonstrated anti-inflammatory impact in vivo and in vitro. To date, the effect of RNO on the synthetic function of airway smooth muscle (ASM) cells is unknown. We address this herein and investigate the effect of RNO on β2-adrenoceptor-mediated, cAMPdependent responses in ASM cells in vitro, and whether RNO enhances steroid-induced repression of inflammation. RNO (0.001-1000 nM) alone had no effect on AMP production from ASM cells, and significant potentiation of the long-acting β2-agonist formoterol-induced cAMP could only be achieved at the highest concentration of RNO tested (1000 nM). At this concentration, RNO exerted a small, but not significantly different, potentiation of formoterolinduced expression of anti-inflammatory mitogen-activated protein kinase phosphatase 1 (MKP-1). Consequently, tumor necrosis factor (TNF)-induced IL-8 secretion was unaffected by RNO in combination with formoterol. However, as there was the potential for PDE4 inhibitors and LABAs to interact with corticosteroids to achieve superior anti-inflammatory efficacy, we examined whether RNO, alone or in combination with formoterol, enhanced the antiinflammatory effect of dexamethasone by measuring the impact on IL-8 secretion. While RNO alone did not significantly enhance cytokine repression achieved with steroids; RNO in combination with formoterol significantly enhanced the anti-inflammatory effect of dexamethasone in ASM cells. This was linked to increased MKP-1 expression in ASM cells, suggesting a molecular mechanism responsible for augmented anti-inflammatory actions of combination therapeutic approaches that include RNO.