The response of flat isotropic rectangular panels reinforced in the directions parallel to the edges and subjected to air blast loading is considered. The solution is obtained by assumption that the stiffeners can be smeared out over the panel. The problem is reduced to a single differential equation for the amplitude of transverse (out-of-plane) deflection which can be integrated analytically or numerically. Then the displacements and stresses in the panel and stiffeners can be determined. The effects of the panel geometry and the blast overpressure are illustrated in numerical examples.