By analyzing experimental data in the literature, the activation energy H for slip in body-centered cubic metals is found to approximately obey the simple relation H≈0.1 μb3(1-t)2, where t is the applied stress normalized by the zero-temperature Peierls stress, μ is the <111> shear modulus, and b the 1/2<111> Burgers vector. Such universal relation is explained by analyzing the activation processes of kink-pair generation and expansion along threefold screw dislocations using the generalized Peierls–Nabarro model [A. H. W. Ngan, J. Mech. Phys. Solids 45, 903 (1997)]. The model also predicts qualitatively the general form of the orientation dependence of Peierls stress at zero temperature. © 1999 American Institute of Physics.