Angle-resolved photoemission is used to determine the energy bands of permalloy (Ni0.8Fe0.2) and compare them to Ni, Co, and Cu. The energy and momentum resolution (approximate to 0.01 eV and approximate to 0.01 Angstrom(-1)) is high enough to resolve the magnetically split bands at the Fermi level that are responsible for spin-dependent conductivity and tunneling. For the Sigma(1) band we find the magnetic exchange splittings delta E-ex = 0.27 eV (0.23 eV for Ni), delta k(ex) = 0.16 +/- 0.02 Angstrom(-1) (0.12 +/- 0.01 Angstrom(-1) for Ni), the Fermi velocity upsilon(F up arrow) = (0.22 +/- 0.02) 10(6) m/s (0.28 x 10(6) m/s for Ni, 0.33 x 10(6) m/s for fcc Co), and the widths delta k(up arrow) less than or equal to 0.11 Angstrom(-1) and delta k(down arrow) = 0.24 Angstrom(-1). Compared to Ni, permalloy features a 27% larger magnetic splitting of the Fermi surface and an extremely short mean free path of 4-8 Angstrom for minority spins. (C) 1998 American Institute of Physics. [S0003-6951(98)01249-2].