  We consider the local properties of the Yb3+ ion in the crystal electric
field in the Kondo lattice compounds YbRh2Si2 and YbIr2Si2. On this basis we
have calculated the magnetic susceptibility taking into account the Kondo
interaction in the simplest molecular field approximation. The resulting
Curie-Weiss law and Van Vleck susceptibilities could be excellently fitted to
experimental results in a wide temperature interval where thermodynamic and
transport properties show non-Fermi-liquid behaviour for these materials.
