The structural integrity of the alveolar monolayer, which is compromised during lung inflammation, is determined by the balance between cell-cell and cell-matrix tethering forces and the centripetal forces owing to cell viscoelasticity and contraction. Dexamethasone is an anti-inflammatory glucocorticoid with protective effects in lung injury. To determine the effects of Dexamethasone on the stiffness and contractility of alveolar epithelial cells. Cell stiffness (G') and average traction exerted by the cell (T) were measured by magnetic twisting cytometry and by traction microscopy, respectively. A549 cells were treated 24 h with Dexamethasone (1 mu M) or vehicle (control). G' and T were measured before and 5 min after challenge with the inflammatory mediator Thrombin (0.5 U/ml). Changes induced by Dexamethasone in actin cytoskeleton polymerization were assessed by the fluorescent ratio between F-actin and G-actin obtained by staining cells with phalloidin and DNase I. Dexamethasone significantly increased G' and T by 56% (n = 11; p < 0.01) and by 80% (n = 17; p < 0.05), respectively. Dexamethasone also increased F/G-actin ratio from 2.68 +/- 0.07 to 2.96 +/- 0.09 (n = 10; p < 0.05). The relative increase in stiffness and contraction induced by Thrombin in control cells was significantly (p < 0.05) reduced by Dexamethasone treatment: from 190 to 98% in G' and from 318 to 105% in T. The cytoskeleton remodelling and the increase in cell stiffness and contraction induced by Dexamethasone could account for its protective effect in the alveolar epithelium when subjected to inflammatory challenge.