A simple procedure for the evaluation of the increase or decrease (sensitivity) of static and dynamic (flutter) buckling loads of structures in the presence of small geometrical imperfections is presented. The computational model considers plane elastic structures modelled by straight beam elements. The loading systems cam be conservative or non-conservative. The matrix formulation includes the usual elastic stiffness, mass, and geometric matrices. The algorithm implemented herein evaluates the classical critical load. In addition, the imperfections are taken into account by an imperfection matrix, which results from the change in the elastic stiffness due to small deviations of geometry (small rotations of the elements). Examples are presented to illustrate the technique developed herein and to investigate the buckling loads of some basic structures: Roorda´s frame, Euler´s column, Beck´s column, circular arch, and beam on elastic foundation (analogous to axissimetric deformation of cylindrical shell). It is concluded that the use of the proposed imperfection matrix can provide valuable qualitative information on the sensitivity of the buckling load to imperfections.