  We study the dependence of magnetic interactions and Curie temperature in
Ni(1+x)MnSb system on the Ni concentration within the framework of the
density-functional theory. The calculation of the exchange parameters is based
on the super-cell and frozen-magnon approaches. The Curie temperatures, Tc, are
calculated within the random-phase approximation. In agreement with experiment
we obtain decrease of the Curie temperature with increasing Ni content.
