1 Symmetry of Tangent Stiffness Matrices of 3D Elastic Frame a B.A. Izzuddin 2 In their paper, the authors contend to have resolved the issues concerning the symmetry of the tangent stiffness matrix for spatial elastic beam elements and frames, suggesting that the element tangent stiffness matrix is invariably asymmetric. Furthermore, they suggest that an asymmetric geometric stiffness 'correction' matrix is required for the detection of the lowest buckling mode of a space dome, citing the failure of several other researchers, including the discusser (Izzuddin and Elnashai, 1993), to detect this mode. The discusser has two contributions to make in connection with the aforementioned claims of the authors. 1. Asymmetry of Element Tangent Stiffness Matrices In order to generalise regarding the symmetry of the tangent stiffness matrix of spatial elastic beam elements and frames, an unambiguous definition of the 'scope' of the tangent stiffness matrix is required, which is not provided by the authors. This particularly concerns the nature of 'applied' loading (particularly moments) and system freedoms (particularly rotations) which the tangent stiffness matrix is associated with. More clearly, the system tangent stiffness matrix (K) can be considered to reflect the infinitesimal variation of out-of-balance forces and moments (G) with system translational and rotational freedoms (U), as expressed by: K i,j = ∂G i ∂U j (1) a February, 1999, Journal of Engineering Mechanics, Vol. 125, No.2, by L.H. Teh and M.J. Clarke (Technical Note No. 14141) 2 Lecturer in Engineering Computing, Department of Civil and Environmental Engineering, Imperial College, London SW7 2BU, U.K.