Structural frames designed or proportioned to resist seismic forces must possess adequate ductility to redistribute internal forces or have needed energy absorbing capability. This paper addresses the interaction effects of a steel member's plate slenderness values and its lateral slenderness on rotation capacity. It is shown that members with slenderness values close to the limits specified by the codes of practice may not be able to redistribute moments adequately under seismic loading. A critical value for the lateral slenderness is proposed to be used with current local buckling rules prescribed in North American standards for a structure to develop its full ductility potential.