  We show, when $G$ is a nilpotent or reductive Lie group, that the entropy of
any surjective endomorphism coincides with the entropy of its restriction to
the toral component of the center of $G$. In particular, if $G$ is a
semi-simple Lie group, the entropy of any surjective endomorphism always
vanishes. Since every compact group is reductive, the formula for the entropy
of a endomorphism of a compact group reduces to the formula for the entropy of
an endomorphism of a torus.
