We discuss the present status of the first-principles electronic-structure calculations for defect energies in metals. The calculations apply density functional theory in the generalized-gradient approximation of Perdew and Wang, together with a full-potential version of Korringa-Kohn-Rostoker Green's function method, developed by the Julich group. It is shown that: (1) the present calculations reproduce very well the experimental results for vacancy formation energies in metals, as well as the bulk properties such as equilibrium lattice parameters and bulk moduli of metals; and (2) the type of the phase diagram of a binary A-B alloy can be characterized by the interaction energies between a pair of impurity B (A) atoms in the host metal A (B). The observed temperature dependence of the solid solubility limit of Rh in Pd is also reproduced very well by the free-energy calculations based on the cluster variation method with the pair- (up to the eighth neighbor) and many-body (up to a tetrahedron of first-nearest neighbors) interaction energies, all of which are determined by the present first-principles calculations. (C) 2001 Elsevier Science B.V. All rights reserved.