-Rosiglitazone (RGZ), a peroxisome proliferator-activated receptor-␥ (PPAR␥) ligand, is a novel dilator of small airways in mouse precision cut lung slices (PCLS). In this study, relaxation to RGZ and -adrenoceptor agonists were compared in trachea from naïve mice and guinea pigs and trachea and PCLS from a mouse model of chronic allergic airways disease (AAD). Airways were precontracted with methacholine before addition of PPAR␥ ligands [RGZ, ciglitazone (CGZ), or 15-deoxy-⌬12,14 -prostaglandin J2 (15-deoxy-PGJ2)] or -adrenoceptor agonists (isoprenaline and salbutamol). The effects of T0070907 and GW9662 (PPAR␥ antagonists) or epithelial removal on relaxation were assessed. Changes in force of trachea and lumen area in PCLS were measured using preparations from saline-challenged mice and mice sensitized (days 0 and 14) and challenged with ovalbumin (3 times/wk, 6 wk). RGZ and CGZ elicited complete relaxation with greater efficacy than -adrenoceptor agonists in mouse airways but not guinea pig trachea, while 15-deoxy-PGJ2 did not mediate bronchodilation. Relaxation to RGZ was not prevented by T0070907 or GW9662 or by epithelial removal. RGZ-induced relaxation was preserved in the trachea and increased in PCLS after ovalbumin-challenge. Although RGZ was less potent than -adrenoceptor agonists, its effects were additive with salbutamol and isoprenaline and only RGZ maintained potency and full efficacy in maximally contracted airways or after allergen challenge. Acute PPAR␥-independent, epithelial-independent airway relaxation to RGZ is resistant to functional antagonism and maintained in both trachea and PCLS from a model of chronic AAD. These novel efficacious actions of RGZ support its therapeutic potential in asthma when responsiveness to -adrenoceptor agonists is limited. allergic airways disease; bronchodilation; lung slice; peroxisome proliferator-activated receptor-␥; rosiglitazone THERE IS INCREASING EVIDENCE that rosiglitazone (RGZ) and other agonists of peroxisome proliferator-activated receptor-␥ (PPAR␥) may offer therapeutic benefit in asthma. Numerous studies suggest that PPAR␥ ligands can inhibit allergen-induced inflammation and the development of airway remodeling and airway hyperresponsiveness (AHR) in vivo (reviewed in Ref. 8), as well as exert direct dilator effects on airway smooth muscle (ASM) in vitro (3, 12).PPAR␥ expression is increased in bronchial biopsies from patients with asthma, including in the epithelial and ASM layers (2). In vitro, human ASM cytokine secretion and proliferation have been shown to be suppressed by the PPAR␥ agonists RGZ and ciglitazone (CGZ) (10,27,30,34,37). However, only some of these anti-inflammatory and antiremodeling activities were inhibited by the selective PPAR␥ antagonist GW9662, suggesting both PPAR␥-dependent and -independent mechanisms (30, 34).The effects of chronic treatment with PPAR␥ ligands have also been examined in mouse models of allergic airway disease (AAD), where sensitization and nebulization with ovalbumin (OVA) causes airway inflamma...