An efficient dynamic analysis method using the modified Lanczos co-ordinates is presented. The proposed method is obtained by applying the modified Lanczos algorithm using Lanczos vectors that satisfy the stiffness-orthonormality condition to the conventional Lanczos co-ordinates method. The modified Lanczos co-ordinates method is more efficient than the conventional method in the case of structures under multi-input loads. The effectiveness of the modified Lanczos co-ordinates method is verified by analysing a numerical example. Copyright (C) 2003 John Wiley Sons, Ltd.