Planar lifting-surface theory is applied to the problem of the loads induced on an infinite aspect-ratio wing by a straight, infinite, free vortex in a subsonic, compressible, freestream; the vortex lies in a plane parallel to the plane of the wing, at a given distance below it, and at an arbitrary angle with the wing centerline. The solution is obtained in the form of an aerodynamic influence function for an infinite aspect-ratio wing in an oblique, sinusoidal gust. The lifting-surface theory kernel function for this wing is presented. This kernel includes as limits the linear, aerodynamic kernel functions for the problems of steady, three-dimensional flow and unsteady, two-dimensional flow, and for the problems of incompressibl e, two-dimensional flow and transonic, three-dimensional flow. An approximate analytic expression is given for the lift influence function, suitable for practical use in the routine calculation of vortex-induced airloads.