A previously proposed member tangent stiffness matrix subjected to elastic-plastic bending and derived from moment-thrust-curvature equations is extended to include the effects induced by the initial crookedness of a member. The shape of the initial geometrical imperfection of the member may be arbitrary and is expressed as an initial curvature in the formulation. A tangent stiffness matrix for initially crooked wide-flange members of elastic-plastic material is constructed and utilized for analyzing inelastic frames with initial geometrical imperfections. For the inelastic frame analyses, an incremental loading procedure is utilized to trace the load-displacement curves for the frames, and the descending branch of the load-displacement curves are obtained by using the modified arc length method of Crisfield. The technique is illustrated by several examples of plane frames loaded beyond their limit points.