Combined experimental and theoretical studies are reported of the Fermi surface, band structure, generalized magnetic susceptibility, electron‐phonon enhancement factor λ and superconducting transition temperature TT of LaB6. Whereas the unusually large λ values, ranging from 1.0 to 2.5, are expected to result in high TT values, TT is observed to be only 0.122°K. These results further emphasize the need for appropriate theoretical formulations for these systems. Copyright © 1975 John Wiley & Sons, Inc.