1. Introduction. In a recent paper [1], J. K. Knowles has established new energy decay estimates for solutions of the biharmonic equation in a semi-infinite strip, subject to nonzero boundary conditions on the near end only. Such estimates, which predict an exponential decay of energy with axial distance from the end, have been used in the analysis of Saint-Venant's principle in plane elastostatics. (See [2] for a review of recent work on principles of Saint-Venant type; for a discussion of earlier results in the linear theory of elasticity, see [3].) These results are also relevant to the study of the spatial evolution of stationary Stokes flows in a semi-infinite parallel plate channel to fully-developed Poiseuille flow [4], Energy decay arguments involving differential inequalities have been employed previously by Knowles [5] in the analysis of Saint-Venant's principle in plane isotropic elastostatics for bounded, simply-connected domains of general shape. Similar arguments were used by Toupin [6] in his investigation of the corresponding issue for the three-dimensional elastic cylinder. In [5] an explicit estimate (lower bound) is obtained for the rate of energy decay with distance from a portion of the domain boundary carrying a self-equilibrated load. A modification of the analysis of [5] was given by Flavin [7], yielding an improved estimate of the decay rate. An alternative argument, leading to the same estimated decay rate as that obtained in [7], has been provided by Oleinik and Yosifian [8], [9].1 The quality of the estimate for the decay rate obtained in [7][8][9] may be tested by comparison with the exact decay rate for the semi-infinite strip problem.2 It turns out that the results of [7][8][9] underestimate the exact value by a factor of nearly one-half.In [1], a third type of argument is employed to establish energy decay for the biharmonic equation in a semi-infinite strip. The new feature contained in [1] is the consideration of a "higher-order energy" in addition to the physical energy associated with the problem. This method provides an improved estimated decay rate over that of [7][8][9], although still underestimating the exact value.