A study is made of the condition of statical equilibrium of plane triangulated (braced) rigidly-jointed frames. It is assumed the frames are loaded centrally at the joints. A nonlinear analysis is made of the elastic behavior of the system. The analysis takes account of the interactions of the members at the continuous joints. It is shown that such frames may, in general, pursue an unstable equilibrium path in the early stages of elastic buckling, and that, initially, the external loads causing buckling must be varied linearly with lateral deflections of the members. The analysis confirms that the critical loading condition, at which buckling can begin, agrees with that given by a conventional eigenvalue treatment of the problem. Tests on simple models made of high-strength steel members (to insure elastic buckling) are described. The results of these tests confirm that an unstable path is possible immediately after buckling. It is commonly assumed that the buckling of a frame occurs in neutral equilibrium; any conclusions based on this assumption should, therefore, be treated cautiously.